1998 Microchip Technology Inc.

Preliminary

DS40183A-page 1

HCS515

FEATURES

Security

· Encrypted storage of manufacturer's code
· Encrypted storage of encoder decryption keys
· Up to seven transmitters can be learned
·

code hopping technology

· Normal and secure learning mechanisms

Operating

· 3.0V--5.5V operation
· Internal oscillator
· Auto bit rate detection

Other

· Stand-alone decoder
· Internal EEPROM for transmitter storage
· Synchronous serial interface
· 1 Kbit user EEPROM
· 14-pin DIP/SOIC package

Typical Applications

· Automotive remote entry systems
· Automotive alarm systems
· Automotive immobilizers
· Gate and garage openers
· Electronic door locks
· Identity tokens
· Burglar alarm systems

Compatible Encoders

· HCS200, HCS300, HCS301, HCS360, HCS361,

HCS410 (PWM Mode)

DESCRIPTION

The Microchip Technology Inc. HCS515 is a code hop-
ping decoder designed for secure Remote Keyless
Entry (RKE) systems. The HCS515 utilizes the pat-
ented K

code hopping system and high security

learning mechanisms to make this a canned solution
when used with the HCS encoders to implement a uni-
directional remote and access control systems. The
HCS515 can be used as a stand-alone decoder or in
conjunction with a microcontroller.

PACKAGE TYPE

BLOCK DIAGRAM

The manufacturer's code, encoder decryption keys,
and synchronization information are stored in
encrypted form in internal EEPROM. The HCS515
uses the S_DAT and S_CLK inputs to communicate
with a host controller device.

The HCS515 operates over a wide voltage range of
3.0 volts to 5.5 volts. The decoder employs automatic
bit-rate detection, which allows it to compensate for
wide variations in transmitter data rate. The decoder
contains sophisticated error checking algorithms to
ensure only valid codes are accepted.

HCS515

PDIP, SOIC

Vdd

Vss

RF_IN

MCLR

S_CLK

S_DAT

67-bit Reception Register

Internal

CONTROL

DECRYPTOR

RFIN

OSCILLATOR

S_DAT
S_CLK

MCLR

EEPROM

EE_DAT

EE_CLK

S0
S1

Code Hopping Decoder

The K

name, K

logo, and logotype are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries.

*Code hopping patents issued in Europe, U. S. A. and R. S.--US:5,517,187; Europe: 0459781

HCS515

DS40183A-page 2

Preliminary

1998 Microchip Technology Inc.

1.0

SYSTEM OVERVIEW

1.1

Key Terms

· Manufacturer's Code A 64-bit word, unique to

each manufacturer, used to produce a unique
encoder decryption key in each transmitter.

· Encoder Decryption Key A 64-bit key, unique for

each transmitter. The encoder decryption key
controls the K

decryption algorithm and is

stored in EEPROM on the decoder device.

· Learn The receiver uses information that is

transmitted to derive the transmitter's encoder
decryption key, decrypt the discrimination value,
and the synchronization counter in learning mode.
The encoder decryption key is a function of the
manufacturer's code and the device serial number
and/or seed value.

The HCS encoders and decoders employ the K

code hopping technology and a K

encryption

algorithm to achieve a high level of security. Code
hopping is a method by which the code transmitted
from the transmitter to the receiver is different every
time a button is pushed. This method, coupled with a
transmission length of 66 bits, virtually eliminates the
use of code `grabbing' or code `scanning'.

1.2

HCS Encoder Overview

The HCS encoders have a small EEPROM array which
must be loaded with several parameters before use.
The most important of these values are:

· An encoder decryption key that is generated at

the time of production

· A 16-bit synchronization counter value

· A 28-bit serial number which is meant to be

unique for every encoder

The manufacturer programs the serial number for each
encoder at the time of production, while the `Key Gen-
eration Algorithm' generates the encoder decryption
key (Figure 1-1). Inputs to the key generation algorithm
typically consist of the encoder's serial number and a
64-bit manufacturer's code, which the manufacturer
creates.

The 16-bit synchronization counter is the basis for the
transmitted code changing for each transmission and is
updated each time a button is pressed. Because of the
complexity of the K

encryption algorithm, a

change in one bit of the synchronization counter value
will result in a large change in the actual transmitted
code. There is a relationship (Figure 1-2) between the
encoder decryption key values in EEPROM and how
they are used in the encoder. Once the encoder
detects that a button has been pressed, the encoder
reads the button and updates the synchronization
counter. The synchronization value is then combined
with the encoder decryption key in the K

encryption algorithm, and the output is 32 bits of
encrypted information. This data will change with every
button press, hence, it is referred to as the code hop-
ping portion of the code word. The 32-bit code hopping
portion is combined with the button information and the
serial number to form the code word transmitted to the
receiver.

FIGURE 1-1:

CREATION AND STORAGE OF ENCRYPTION KEY DURING PRODUCTION

Note:

The manufacturer code is a pivotal part of
the system's overall security. Conse-
quently, all possible precautions must be
taken and maintained for this code.

Transmitter

Manufacturer's

Serial Number or

Code

Encryption

Key

Generation

Algorithm

Serial Number

Encryption Key

Sync Counter

.
.

HCS515 EEPROM Array

Seed

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 3

1.3

HCS Decoder Overview

Before a transmitter and receiver can work together,
the receiver must first `learn' and store certain informa-
tion from the transmitter. This information includes a
`check value' of the serial number, the encoder decryp-
tion key, and current synchronization counter value.

When a valid formatted message is detected, the
receiver first compares the serial number. If the serial
number check value is from a learned transmitter, the
message is decrypted. Next, the receiver checks the
decrypted synchronization counter value against what
is stored in memory. If the synchronization counter
value is verified, then a valid transmission message is
sent. Figure 1-3 shows the relationship between some
of the values stored by the receiver and the values
received from the transmitter.

FIGURE 1-2:

BASIC OPERATION OF A CODE HOPPING TRANSMITTER (ENCODER)

FIGURE 1-3:

BASIC OPERATION OF A CODE HOPPING RECEIVER (DECODER)

Algorithm

Button Press

Information

Encryption

EEPROM Array

32 Bits of

Encrypted Data

Serial Number

Transmitted Information

Encoder Decryption Key

Sync. Counter Value

Serial Number

Button Press
Information

EEPROM Array

Encoder Decryption Key

32 Bits of

Encrypted Data

Serial Number

Received Information

Decrypted

Synchronization

Counter

Check for

Match

Check for

Match

Algorithm

Decryption

Sync. Counter Value

Serial Number

Manufacturer Code

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 5

3.0

DECODER OPERATION

3.1

Learning a Transmitter to a Receiver
(Normal or Secure Learn)

Before the transmitter and receiver can work together,
the receiver must first `learn' and store the following
information from the transmitter in EEPROM:

· A check value of the serial number
· The encoder decryption key
· The current synchronization counter value

The decoder must also store the manufacturer's code
(Section 1.2) in protected memory. This code will
typically be the same for all of the decoders in a sys-
tem.

The HCS515 has seven memory slots, and, conse-
quently, can store up to seven transmitters. During the
learn procedure, the decoder searches for an empty
memory slot for storing the transmitter's information.
When all of the memory slots are full, the decoder will
overwrite the last transmitter's information. To erase all
of the memory slots at once, use the ERASE_ALL
command (C3H).

3.1.1

LEARNING PROCEDURE

Learning is initiated by sending the ACTIVATE_LEARN
(D2H) command to the decoder. The decoder acknowl-
edges reception of the command by pulling the data
line high.

For the HCS515 decoder to learn a new transmitter, the
following sequence is required:

Activate the transmitter once.

Activate the transmitter a second time. (In
secure learning mode, the seed transmission
must be transmitted during the second stage of
learn by activating the appropriate buttons on
the transmitter.)

The HCS515 will transmit a learn-status string,
indicating that the learn was successful.

The decoder has now learned the transmitter.

Repeat steps 1-3 to learn up to seven
transmitters

Note 1:

Learning will be terminated if two
nonsequential codes were received or if two
acceptable codes were not decoded within
30 seconds.

If more than seven transmitters are learned,
the new transmitter will replace the last
transmitter learned. It is, therefore, not pos-
sible to erase lost transmitters by
repeatedly learning new transmitters. To
remove lost or stolen transmitters,
ERASE_ALL transmitters and relearn all
available transmitters.

Learning a transmitter with an encoder
decryption key that is identical to a transmit-
ter already in memory replaces the existing
transmitter. In practice, this means that all
transmitters should have unique encoder
decryption keys. Learning a previously
learned transmitter does not use any addi-
tional memory slots.

The following checks are performed by the decoder to
determine if the transmission is valid during learn:

· The first code word is checked for bit integrity.
· The second code word is checked for bit integrity.
· The encoder decryption key is generated accord-

ing to the selected algorithm.

· The hopping code is decrypted.

· The discrimination value is checked.

· If all the checks pass, the key, serial number

check value, and synchronization counter values
are stored in EEPROM memory.

Figure 3-1 shows a flow chart of the learn sequence.

FIGURE 3-1:

LEARN SEQUENCE

Enter Learn

Mode

Wait for Reception

of Second

Compare Discrimination

Value with Serial Number

Use Generated Key

to Decrypt

Equal?

Sync. counter value

Encoder decryption key

Exit

Learn successful. Store:

Learn

Unsuccessful

Yes

Wait for Reception

of a Valid Code

Non-Repeated

Valid Code

Generate Key

from Serial Number/

Seed Value

Serial number check value

HCS515

DS40183A-page 6

Preliminary

1998 Microchip Technology Inc.

3.2

Validation of Codes

The decoder waits for a transmission and checks the
serial number to determine if it is a learned transmitter.
If it is, it takes the code hopping portion of the transmis-
sion and decrypts it, using the encoder decryption key.
It uses the discrimination value to determine if the
decryption was valid. If everything up to this point is
valid, the synchronization counter value is evaluated.

3.3

Validation Steps

Validation consists of the following steps:

Search EEPROM to find the Serial Number
Check Value Match

Decrypt the Hopping Code

Compare the 10 bits of the discrimination value
with the lower 10 bits of serial number

Check if the synchronization counter value falls
within the first synchronization window.

Check if the synchronization counter value falls
within the second synchronization window.

If a valid transmission is found, update the
synchronization counter, else use the next
transmitter block, and repeat the tests.

FIGURE 3-2:

DECODER OPERATION

3.4

Synchronization with Decoder

The K

technology features a sophisticated

synchronization technique (Figure 3-3) which does not
require the calculation and storage of future codes. If
the stored synchronization counter value for that
particular transmitter and the synchronization counter
value that was just decrypted are within a formatted
window of 16, the counter is stored, and the command
is executed. If the synchronization counter value was
not within the single operation window, but is within the
double operation window of the 16K window, the
transmitted synchronization counter value is stored in a
temporary location, and the decoder goes back to wait-
ing for another transmission. When the next valid
transmission is received, it will check the new
synchronization counter value with the one in tempo-
rary storage. If the two values are sequential, it is
assumed that the counter had just gotten out of the
single operation `window', but is now back in synchroni-
zation, so the new synchronization counter value is
stored, and the command is executed. If a transmitter
has somehow gotten out of the double operation
window, the transmitter will not work and must be
relearned. Since the entire window rotates after each
valid transmission, codes that have been used become
part of the `blocked' (48K) codes and are no longer
valid. This eliminates the possibility of grabbing a previ-
ous code and retransmitting to gain entry.

FIGURE 3-3:

SYNCHRONIZATION WINDOW

Transmission

Received?

Does

Ser # Check Val

Match?

Decrypt Transmission

decryption

valid?

counter within

16?

counter within

16K?

Update

Counter

Execute

Command

Save Counter

in Temp Location

Start

Yes

and

Blocked

Entire Window
rotates to eliminate
use of previously
used codes

Current

Position

(48K Codes)

Double
Operation
(16K Codes)

Single
Operation
Window
(16 Codes)

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 7

4.0

INTERFACING TO A
MICROCONTROLLER

The HCS515 interfaces to a microcontroller via a syn-
chronous serial interface. A clock and data line are
used to communicate with the HCS515. The microcon-
troller controls the clock line. There are two groups of
data transfer messages. The first is from the decoder
whenever the decoder receives a valid transmission.
The decoder signals reception of a valid code by taking
the data line high (maximum of 500 ms) The microcon-
troller then services the request by clocking out a data
string from the decoder. The data string contains the
function code, the status bit, and block indicators. The
second is from the controlling microcontroller to the
decoder in the form of a defined command set.

Figure 4-1 shows the HCS515 decoder and the I/O
interface lines necessary to interface to a microcontrol-
ler.

4.1

Valid Transmission Message

The decoder informs the microcontroller of a valid
transmission by taking the data line high for up to
500 ms. The controlling microcontroller must acknowl-
edge by taking the clock line high. The decoder then
takes the data line low. The microcontroller can then
begin clocking a data stream out of the HCS515. The
data stream consists of:

· Start bit `0'.
· 2 status bits [REPEAT, VLOW].
· 4-bit function code [S3 S2 S1 S0].

· Stop bit `1'.

· 4 bits indicating the number of transmitters

learned into the decoder [CNT3...CNT0].

· 4 bits indicating which block was used

[TX3...TX0].

· 64 bits of the received transmission with the hop-

ping code decrypted.

The decoder will terminate the transmission of the data
stream at any point where the clock is kept low for
longer than 1 ms.Therefore, the microcontroller can
only clock out the required bits. A maximum of 80 bits
can be clocked out of the decoder.

FIGURE 4-1:

HCS515 DECODER AND I/O INTERFACE LINES

FIGURE 4-2:

DECODER VALID TRANSMISSION MESSAGE

Note:

Data is always clocked in/out Least
Significant Bit (LSB) first.

RF DATA

SYNC CLOCK

SYNC DATA

S1 OUTPUT

HCS515

MCLR

RF_IN

S_CLK

S_DAT

MICRO RESET

S0 OUTPUT

Decoder Signal Valid

CLKH

Cii

ACT

DHI

CLA

Received String

S_DAT

TX0

TX3

RX63

REPT V

LOW

CNT0

CNT3

RX0

RX1

RX62

S_CLK

Information

ACK

CLKH

CLKL

Transmission

HCS515

DS40183A-page 8

Preliminary

1998 Microchip Technology Inc.

4.2

Command Mode

4.2.1

MICROCONTROLLER COMMAND MODE
ACTIVATION

The microcontroller command consists of four parts.
The first part activates the command mode, the second
part is the actual command, the third is the address
accessed, and the last part is the data. The microcon-
troller starts the command by taking the clock line high
for up to 500 ms. The decoder acknowledges the start-
up sequence by taking the data line high. The micro-
controller takes the clock line low, after which the
decoder will take the data line low, tri-state the data line
and wait for the command to be clock in. The data must
be set up on the rising edge and will be sampled on the
falling edge of the clock line.

4.2.2

COLLISION DETECTION

The HCS515 uses collision detection to prevent
clashes between the decoder and microcontroller.
Whenever the decoder receives a valid transmission
the following sequence is followed:

· The decoder first checks to see if the clock line is

high. If the clock line is high, the valid transmis-
sion notification is aborted, and the microcontrol-
ler command mode request is serviced.

· The decoder takes the data line high and checks

that the clock line doesn't go high within 50

s. If

the clock line goes high, the valid transmission
notification is aborted and the command mode
request is serviced.

· If the clock line goes high after 50

s but before

500 ms, the decoder will acknowledge by taking
the data line low.

· The microcontroller can then start to clock out the

80-bit data stream of the received transmission.

FIGURE 4-3:

MICROCONTROLLER COMMAND MODE ACTIVATION

MSB

Command Byte

Start Command

CLKL

CLKH

LSB

START

CMD

DATA

Address Byte

Data Byte

ADDR

REQ

RESP

CLK

C Data

HCS515

Data

MSB

LSB

MSB

LSB

ACK

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 9

4.2.3

COMMAND ACTIVATION TIMES

The command activation time (Table 4-1) is defined as
the maximum time the microcontroller has to wait for a
response from the decoder. The decoder will abort and
service the command request. The response time
depends on the state of the decoder when the com-
mand mode is requested.

4.2.4

DECODER COMMANDS

The command byte specifies the operation required by
the controlling microcontroller. Table 4-2 lists the com-
mands.

TABLE 4-1:

COMMAND ACTIVATION TIMES

Decoder State

Min

Max

While receiving transmissions

2 1/2 BPW

MAX

= 2.7 ms

During the validation of a received transmission

3 ms

During the update of the sync counters

40 ms

During learn

170 ms

TABLE 4-2:

DECODER COMMANDS

Instruction

Command Byte

Operation

READ

Read a byte from user EEPROM

WRITE

Write a byte to user EEPROM

ACTIVATE_LRN

Activate a learn sequence on the decoder

ERASE_ALL

Activate an erase all function on the decoder

PROGRAM

Program manufacturer's code and configuration byte

HCS515

DS40183A-page 10

Preliminary

1998 Microchip Technology Inc.

4.2.5

READ BYTE/S FROM USER EEPROM

The read command (Figure 4-4) is used to read bytes
from the user EEPROM. The offset in the user
EEPROM is specified by the address byte which is
truncated to seven bits (C to D). After the address, a
dummy byte must be clocked in (D to E). The EEPROM
data byte is clocked out on the next rising edge of the
clock line with the least significant bit first (E to F).
Sequential reads are possible by repeating sequence E
to F within 1 ms after the falling edge of the previous
byte's Most Significant Bit (MSB) bit. During the
sequential read, the address value will wrap after 128
bytes. The decoder will terminate the read command if
no clock pulses are received for a period longer than
1.2 ms.

4.2.6

WRITE BYTE/S TO USER EEPROM

The write command (Figure 4-5) is used to write a loca-
tion in the user EEPROM. The address byte is trun-
cated to seven bits (C to D). The data is clocked in least
significant bit first. The clock line must be asserted to
initiate the write. Sequential writes of bytes are possible
by clocking in the byte and then asserting the clock line
(D F). The decoder will terminate the write command
if no clock pulses are received for a period longer than
1.2 ms After a successful write sequence the decoder
will acknowledge by taking the data line high and keep-
ing it high until the clock line goes low.

4.2.7

ERASE ALL

The erase all command (Figure 4-6) erases all the
transmitters in the decoder. After the command and two
dummy bytes are clocked in, the clock line must be
asserted to activate the command. After a successful
completion of an erase all command, the data line is
asserted until the clock line goes low.

FIGURE 4-4:

READ BYTES FROM USER EEPROM

FIGURE 4-5:

WRITE BYTES TO USER EEPROM

FIGURE 4-6:

ERASE ALL

Decoder DATA

MSB

Command Byte

Start Command

LSB

Address Byte

Dummy Byte

CLK

C DATA

Data Byte

MSB

LSB

MSB

LSB

MSB

LSB

Decoder DATA

MSB

Command Byte

Start Command

LSB

Address Byte

Data Byte

CLK

C DATA

Acknowledge

MSB

LSB

MSB

LSB

ACK

RESP

ACK

Decoder DATA

MSB

Command Byte

Start Command

LSB

ERA

Subcommand Byte

Dummy Byte

CLK

C DATA

Acknowledge

MSB

LSB

MSB

LSB

ACK

RESP

ACK

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 11

4.2.8

ACTIVATE LEARN

The activate learn command (Figure 4-7) is used to
activate a transmitter learning sequence on the
decoder. The command consists of a command mode
activation sequence, a command byte, and two dummy
bytes. The decoder will respond by taking the data line
high to acknowledge that the command was valid and
that learn is active.

Upon reception of the first transmission, the decoder
will respond with a learn status message (Figure 4-8).

During learn, the decoder will acknowledge the recep-
tion of the first transmission by taking the data line high
for 60 ms. The controlling microcontroller can clock out
at most eight bits, which will all be zeros. All of the bits
of the status byte are zero, and this is used to distin-
guish between a learn time-out status string and the
first transmission received string. The controlling micro-
controller must ensure that the clock line does not go
high 60 ms after the falling edge of the data line, for this
will terminate learn.

Upon reception of the second transmission, the
decoder will respond with a learn status message
(Figure 4-9).

The learn status message after the second transmis-
sion consists of the following:

· 1 start bit.
· The function code [S3:S0] of the message is zero,

indicating that this is a status string.

· The RESULT bit indicates the result of the learn

sequence. The RESULT bit is set if successful
and cleared otherwise.

· The OVR bit will indicate whether an exiting trans-

mitter is over written. The OVR bit will be set if an
existing transmitter is learned over.

· The [CNT3...CNT0] bits will indicate the number

of transmitters learned on the decoder.

· The [TX3...TX0] bits indicate the block number

used during the learning of the transmitter.

FIGURE 4-7:

LEARN MODE ACTIVATION

FIGURE 4-8:

LEARN STATUS MESSAGE AFTER FIRST TRANSMISSION

FIGURE 4-9:

LEARN STATUS MESSAGE AFTER SECOND TRANSMISSION

Decoder DATA

MSB

Command Byte

Start Command

LSB

LRN

Dummy Byte

CLK

C DATA

Acknowledge

MSB

LSB

MSB

LSB

ACK

RESP

ACK

Command Request

CLKL

CLKH

CLL

DHI

CLA

CLH

CLK

Decoder

Status Byte

Data

Communications Request

CLKL

CLKH

ACT

Cii

CLL

DHI

CLA

CLH

CLK

Decoder

TX0

TX3

RX63

OVR RSLT

CNT0

CNT3

RX0

RX1

RX62

Learn Status Bits

Decoded Tx

Data

HCS515

DS40183A-page 12

Preliminary

1998 Microchip Technology Inc.

4.3

Stand-alone Mode

The HCS515 decoder can also be used in stand-alone
applications. The HCS515 will activate the data line for
up to 500 ms if a valid transmission was received, and
this output can be used to drive a relay circuit. To acti-
vate learn or erase all commands, a button must be
connected to the CLK input. User feedback is indicated
on an LED connected to the DATA output line. If the
CLK line is pulled high, using the learn button, the LED
will switch on. After the CLK line is kept high for longer
than 2 seconds, the decoder will switch the LED line off,
indicating that learn will be entered if the button is
released. If the CLK line is kept high for another 6 sec-
onds, the decoder will activate an ERASE_ALL Com-
mand.

Learn mode can be aborted by taking the clock line
high until the data line goes high (LED switches on).
During learn, the data line will give feedback to the user
and, therefore, must not be connected to the relay drive
circuitry.

After taking the clock low and before a transmitter is
learn, any low-to-high change on the clock line may ter-
minate learn. This has learn implications when a switch
with contact bounce is used.

4.4

Erase All Command and Erase
Command

The Table 4-3 describes two versions of the Erase All
command.

Subcommand 01 can be used where a transmitter with
permanent status is implemented in the microcontroller
software. Use of subcommand 01 ensures that the per-
manent transmitter remains in memory even when all
other transmitters are erased. The first transmitter
learned after any of the following events is the first
transmitter in memory and becomes the permanent
transmitter:

Programming of the manufacturer's code.

Erasing of all transmitters
(subcommand 00 only).

4.5

Test Mode

A special test mode is activated after:

Programming of the manufacturer's code.

Erasing of all transmitters.

Test mode can be used to test a decoder before any
transmitters are learned on it. Test mode enables test-
ing of decoders without spending the time to learn a
transmitter. Test mode is terminated after the first suc-
cessful learning of an ordinary transmitter. In test
mode, the decoder responds to a test transmitter. The
test transmitter has the following properties:

Encoder decryption key = manufacturer's code.

Serial number = any value.

Discrimination bits = lower 10 bits of the serial
number.

Synchronization counter value = any value
(synchronization information is ignored).

Because the synchronization counter value is ignored
in test mode, any number of test transmitters can be
used, even if their synchronization counter values are
different.

Note:

The REPS bit must be cleared in the con-
figuration byte in stand-alone mode.

TABLE 4-3:

ERASE ALL COMMAND

Command

Byte

Subcommand

Byte

Description

Erase all
transmitters.

Erase all transmit-
ters except 1. The
first transmitter in
memory is not
erased.

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 13

4.6

Power Supply Supervisor

Reliable operation of the HCS515 requires that the
contents of the EEPROM memory be protected against
erroneous writes. To ensure that erroneous writes do

not occur after supply voltage "brown-out" conditions,
the use of a proper power supply supervisor device is
imperative (Figure 4-11 and Figure 8-4).

FIGURE 4-10: STAND-ALONE MODE LEARN/ERASE-ALL TIMING

FIGURE 4-11: TYPICAL STAND-ALONE APPLICATION CIRCUIT

DATA

Erase-All Activation

REQ

LRN

CLK

Learn Activation

ERA

Successful

LRN

OUTPUT

RELAY SPST

Vcc

S1
LEARN

Q2
NPN

10K

D1
LED

R2
10K

Vcc

G
N
D

U3
Brown-out Circuit

NC
NC
V

HCS515

S1
MCLR
NC

NC
NC

RF_IN

S_CLK

S_DAT

1
2
3
4
5
6
7

10K

Vcc

10K

ANT1

RF Circuit

HCS515

DS40183A-page 14

Preliminary

1998 Microchip Technology Inc.

5.0

DECODER PROGRAMMING

The memory is divided between system memory that stores the transmitter information (read protected) and user mem-
ory (read/write). Commands to access the user memory are described in Sections 4.2.5 and 4.2.6.

The following information stored in system memory needs to be programmed before the decoder can be used:

· 64-bit manufacturer's code

· Decoder configuration byte

5.1

Configuration Byte

The decoder is configured during initialization by setting the appropriate bits in the configuration byte. The following table
list the options:

5.1.1

LRN_MODE

LRN_MODE selects between two learning modes. With LRN_MODE = 0, the normal (serial number derived) mode is
selected; with LRN_MODE=1, the secure (seed derived) mode is selected. See Section 6.0 for more detail on learning
modes.

5.1.2

REPEAT

The HCS515 can be configured to indicate repeated transmissions. In a stand-alone configuration, repeated transmis-
sions must be disabled.

Note 1: These memory locations are read protected and can only be written to using the program command with

the device powered up.

2: The contents of the system memory is encrypted by a unique 64-bit key that is stored in the HCS515. To

initialize the system memory, the HCS515's program command must be used.

Bit

Mnemonic

Description

LRN_MODE

Learning mode selection

LRN_MODE = 0--Normal Learn
LRN_MODE = 1--Secure Learn

Not Used

Reserved

REPEAT

Repeat Transmission enable

0 = Disable
1 = Enabled

Not Used

Reserved

Not Used

Reserved

Not Used

Reserved

Not Used

Reserved

Not Used

Reserved

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 15

5.2

Programming Waveform

The programming command consists of the following:

· Command Request Sequence (A to B)
· Command Byte (B to C)
· Configuration Byte (C to D)
· Manufacturer's Code Eight Data Bytes (D to G)
· Activation and Acknowledge Sequence (G to H)

5.3

Programming Data String

A total of 80 bits are clocked into the decoder. The 8-bit
command byte is clocked in first, followed by the 8-bit
configuration byte and the 64-bit manufacturer's code.
The data must be clocked in Least Significant Bit (LSB)
first. The decoder will then encrypt the manufacturer's
code using the decoder's unique 64-bit EEPROM
encoder decryption key. After completion of the pro-
gramming EEPROM, the decoder will acknowledge by
taking the data line high (G to H). If the data line goes
high within 30 ms after the clock goes high, program-
ming also fails.

FIGURE 5-1:

PROGRAMMING WAVEFORM

DECODER DATA

MSB

Command Byte

Start Command

CLKL

CLKH

LSB

CMD

LSB

Configuration Byte

CLK

C DATA

MSB

DATA

Most Significant Byte

ACK

Acknowledge

MSB

Least Significant Byte

DATA

ADDR

HCS515

DS40183A-page 16

Preliminary

1998 Microchip Technology Inc.

6.0

KEY GENERATION

The HCS515 supports two learning schemes which are selected during the initialization of the system EEPROM. The
learning schemes are:

· Normal learn using the K

decryption algorithm

· Secure learn using the K

decryption algorithm

6.1

Normal (Serial Number derived) Learn using the K

Decryption Algorithm

This learning scheme uses the K

decryption algorithm and the 28-bit serial number of the transmitter to derive

the encoder decryption key. The 28-bit serial number is patched with predefined values as indicated below to form two
32-bit seeds.

SourceH = 60000000 00000000H + Serial Number |

28 Bits

SourceL = 20000000 00000000H + Serial Number |

28 Bits

Then, using the K

decryption algorithm and the manufacturer's code the encoder decryption key is

derived as follows:

KeyH

Upper 32 bits

= F

Decryption

(SourceH) |

64-Bit Manufacturer's Code

KeyL

Lower 32 bits

= F

Decryption

(SourceL) |

64-Bit Manufacturer's Code

6.2

Secure (Seed Derived) Learn using the K

Decryption Algorithm

This scheme uses the secure seed transmitted by the encoder to derive the two input seeds. The decoder always uses
the lower 64 bits of the transmission to form a 60-bit seed. The upper 4 bits are always forced to zero.

For 32-bit seed encoders (HCS200/HCS300/HCS301):

SourceH = Serial Number

Lower 28 bits

SourceL = Seed

32 bits

For 48-bit seed encoders (HCS360/HCS361):

SourceH = Seed

Upper 16 bits

+ Serial Number

Upper 16 bits

with upper 4 bits set to zero

SourceL = Seed

Lower

32 bits

For 60-bit seed encoders (HCS410):

SourceH = Seed

Upper 32 bits

with upper 4 bits set to zero

SourceL = Seed

Lower 32 bits

The K

decryption algorithm and the manufacturer's code is used to derive the encoder decryption key as

follows:

KeyH

Upper 32 bits

= F

Decrypt

(SourceH) |

64 Bit Manufacturer's Code

KeyL

Lower 32 bits

= F

Decrypt

(SourceL) |

64 Bit Manufacturer's Code

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 17

7.0

ENCODERS

7.1

Transmission Format (PWM)

The K

encoder transmission is made up of sev-

eral parts (Figure 7-1). Each transmission begins with
a preamble and a header, followed by the encrypted
and then the fixed data. The actual data is 66/67 bits
which consists of 32 bits of encrypted data and 34/35
bits of non-encrypted data. Each transmission is fol-
lowed by a guard period before another transmission
can begin. The code hopping portion provides up to
four billion changing code combinations and includes
the button status bits (based on which buttons were
activated), along with the synchronization counter
value and some discrimination bits. The non-code hop-
ping portion is comprised of the status bits, the function
bits, and the 28-bit serial number. The encrypted and
non-encrypted combined sections increase the num-
ber of combinations to 7.38 x 10

7.2

Code Word Organization

The HCS encoder transmits a 66/67-bit code word
when a button is pressed. The 66/67-bit word is con-
structed from a code hopping portion and a non-code
hopping portion (Figure 7-2).

The Encrypted Data is generated from four button bits,
two overflow counter bits, ten discrimination bits, and
the 16-bit synchronization counter value.

The Non-encrypted Data is made up from 2 status
bits, 4 function bits, and the 28/32-bit serial number.

FIGURE 7-1:

CODE WORD TRANSMISSION FORMAT

FIGURE 7-2:

CODE WORD ORGANIZATION

LOGIC `0'

LOGIC `1'

Bit

Period

Preamble

Header

Code Hopping Portion

of Transmission

Fixed Portion of
Transmission

Guard

Time

HOP

FIX

Repeat

LOW

(1 bit)

Button Status

S2S1S0S3

(4 bits)

28-bit

Serial

Number

Button Status

S2S1S0S3

(4 bits)

Discrimination

bits (12 bits)

16-bit
Sync.

Counter

Value

CRC1*

CRC0*

3/2 bits

Serial Number and

Button Status (32 bits)

32 bits of Encrypted Data

Encrypted Data

Non-encrypted Data

*HCS360/361

66/67 bits
of Data
Transmitted

HCS515

DS40183A-page 18

Preliminary

1998 Microchip Technology Inc.

8.0

ELECTRICAL CHARACTERISTICS FOR HCS515

Absolute Maximum Ratings

Ambient temperature under bias .............................................................................................................. -40

C to +85

Storage temperature ..............................................................................................................................-65

C to +150

Voltage on any pin with respect to V

(except V

) ........................................................................ -0.6V to V

+0.6V

Voltage on V

with respect to Vss.................................................................................................................. 0 to +7.0V

Total power dissipation (Note) ............................................................................................................................. 700 mW

Maximum current out of V

pin........................................................................................................................... 200 mA

Maximum current into V

pin ............................................................................................................................. 150 mA

Input clamp current, I

< 0 or V

> V

) ........................................................................................................

20 mA

Output clamp current, IOK (V

< 0 or V

) .................................................................................................

20 mA

Maximum output current sunk by any I/O pin ......................................................................................................... 25 mA

Maximum output current sourced by any I/O pin.................................................................................................... 25 mA

Note:

Power dissipation is calculated as follows: P

DIS

= V

x {I

} +

{(V

) x I

} +

l x I

)

NOTICE: Stresses above those listed under "Absolute Maximum Ratings" may cause permanent damage to the

device. This is a stress rating only and functional operation of the device at those or any other conditions above those
indicated in the operation listings of this specification is not implied. Exposure to maximum rating conditions for
extended periods may affect device reliability.

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 19

FIGURE 8-3:

RESET WATCHDOG TIMER, OSCILLATOR START-UP TIMER AND POWER-UP TIMER
TIMING

TABLE 8-1:

DC CHARACTERISTICS

Standard Operating Conditions (unless otherwise stated)
Operating temperature
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

()

Max

Units

Conditions

Supply voltage

3.0

5.5

POR

start voltage to

ensure Reset

Vss

VDD

rise rate to

ensure reset

0.05*

V/ms

Supply current

--
--

1.8
0.3

2.4

OSC

= 4 MHz, V

= 5.5V

Sleep mode (no RF input)

Power Down Current

0.25

= 3.0V, Commercial

0.3

= 3.0V, Industrial

Input low voltage

0.15 V

0.8

between 4.5V and 5.5V

Input high voltage

0.25 V

+ 0.8

Except MCLR = 0.85 V

2.0

between 4.5V and 5.5V

Output low voltage

0.6

= 8.7 mA, V

= 4.5V

Output high voltage

- 0.7

= -5.4 mA, V

= 4.5V

Data in "Typ" column is at 5.0V, 25

C unless otherwise stated. These parameters are for design guidance only and

are not tested.

These parameters are characterized but not tested.

Note:

Negative current is defined as coming out of the pin.

TABLE 8-2:

AC CHARACTERISTICS

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

Conditions

Transmit elemental period

660

Output delay

237

MCLR

MCLR low time

150

Time output valid

150

222

Note:

These parameters are characterized but not tested.

MCLR

I/O Pins

Tov

MCLR

HCS515

DS40183A-page 20

Preliminary

1998 Microchip Technology Inc.

8.1

AC Electrical Characteristics

8.1.1

VALID TRANSMISSION NOTIFICATION

Standard Operating Conditions (unless otherwise specified)"
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

DHI

Command request time

0.0050

500

CLA

Micro request acknowledge time

0.0050

ACK

Decoder Acknowledge time

ACT

Start command mode to
first command bit

1200

CLKH

Clock high time

1000

CLKL

Clock low time

1000

CLK

Clock frequency

500

25000

Data hold time

1000

Note:

These parameters are characterized but not tested.

8.1.2

COMMAND MODE ACTIVATION

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

REQ

Command request time

0.0050

500

RESP

Microcontroller request
acknowledge time

ACK

Decoder acknowledge time

START

Start command mode to first
command bit

1000

CLKH

Clock high time

1000

CLKL

Clock low time

1000

CLK

Clock frequency

500

25000

Data hold time

CMD

Command validate time

ADDR

Address validate time

DATA

Data validate time

Note:

These parameters are characterized but not tested.

8.1.3

READ FROM USER EEPROM COMMAND

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

Decoder EEPROM read time

1000

2000

Note:

These parameters are characterized but not tested.

HCS515

1998 Microchip Technology Inc.

Preliminary

DS40183A-page 21

8.1.4

WRITE TO USER EEPROM COMMAND

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

Write command activation time

1000

ACK

EEPROM write acknowledge time

RESP

Microcontroller acknowledge
response time

1000

ACK

Decoder response
acknowledge time

Note:

These parameters are characterized but not tested.

8.1.5

ERASE ALL COMMAND

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

ERA

Learn command activation time

1000

ACK

Decoder acknowledge time

210

RESP

Microcontroller acknowledge
response time

1000

ACK

Decoder data line low

Note:

These parameters are characterized but not tested.

8.1.6

ACTIVATE LEARN COMMAND IN MICRO MODE

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

LRN

Learn command activation time

1000

ACK

Decoder acknowledge time

RESP

Microcontroller acknowledge
response time

1000

ACK

Decoder data line low

Note:

These parameters are characterized but not tested.

8.1.7

ACTIVATE LEARN COMMAND IN STAND-ALONE MODE

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

REQ

Command request time

100

LRN

Learn command activation time

ERA

Erase-all command activation time

Note:

These parameters are characterized but not tested.

HCS515

DS40183A-page 22

Preliminary

1998 Microchip Technology Inc.

8.1.8

LEARN STATUS STRING

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

DHI

Command request time

500

CLA

Microcontroller command
request time

0.005

500

ACT

Decoder request acknowledge time

CLH

Clock high hold time

1.2

CLL

Clock low hold time

0.020

1.2

CLKH

Clock high time

1000

CLKL

Clock low time

1000

CLK

Clock frequency

500

25000

Data hold time

Note:

These parameters are characterized but not tested.

8.1.9

PROGRAMMING COMMAND

Standard Operating Conditions (unless otherwise specified):
Commercial (C):

+70

Industrial (I):

-40

+85

Symbol

Parameters

Min

Typ

Max

Units

Command request time

500

Decoder acknowledge time

Start command mode to first
command bit

1000

Data line low before tri-stated

CLKH

Clock high time

1000

CLKL

Clock low time

1000

CLK

Clock frequency

500

25000

Data hold time

CMD

Command validate time

ACK

Command acknowledge time

240

Acknowledge respond time

1000

ALW

Data low after clock low

Note:

These parameters are characterized but not tested.

HCS515

DS40183A-page 24

Preliminary

1998 Microchip Technology Inc.

PRODUCT IDENTIFICATION SYSTEM

To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.

Sales and Support

Package:

P = Plastic DIP (300 mil Body), 14-lead

SM = Plastic SOIC (150 mil Body), 14-lead

Temperature

Blank = 0

C to +70

Range:

= 40

C to +85

Device:

HCS515

Code Hopping Decoder

HCS515T

Code Hopping Decoder (Tape and Reel)

HCS515

Data Sheets
Products supported by a preliminary Data Sheet may have an errata sheet describing minor operational differences and recom-
mended workarounds. To determine if an errata sheet exists for a particular device, please contact one of the following:

Your local Microchip sales office.

The Microchip Corporate Literature Center U.S. FAX: (602) 786-7277.

The Microchip's Bulletin Board, via your local CompuServe number (CompuServe membership NOT required).

Information contained in this publication regarding device applications and the like is intended for suggestion only and may be superseded by updates. No representation or warranty
is given and no liability is assumed by Microchip Technology Incorporated with respect to the accuracy or use of such information, or infringement of patents or other intellectual
property rights arising from such use or otherwise. Use of Microchip's products as critical components in life support systems is not authorized except with express written approval
by Microchip. No licenses are conveyed, implicitly or otherwise, under any intellectual property rights. The Microchip logo and name are registered trademarks of Microchip Tech-
nology Inc. in the U.S.A. and other countries. All rights reserved. All other trademarks mentioned herein are the property of their respective companies.

DS40183A-page 28

Preliminary

1998 Microchip Technology Inc.

Printed on recycled paper.

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1/13/98

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