ELM633
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
19200bps miniLIN Monitor
Description
Applications
Block Diagram
1 of 11
Features
ELM633DSB
Connection Diagram
PDIP and SOIC
(top view)
V
DD
V
SS
LIN
XT1
XT2
Rxmode
1
2
3
4
5
6
8
7
RS232Tx
RS232Rx
LIN or `Local Interconnect Network' is a low cost
and relatively simple networking system that is used
predominantly in the automotive world. Recently, it
has been gaining in popularity with proposals to use
it in major appliances as well. For more information,
visit the LIN web site (http://www.lin-subbus.de/).
The ELM633 is a monitoring device designed
for troubleshooting LIN bus systems. It is capable of
continually monitoring a LIN network, translating the
LIN messages to standard ASCII characters, and re-
transmitting them to an RS232 system (personal
computer or PDA) for display and possibly for
analysis. The synchronizing, data formatting, and
checksum calculations are all done for you by the
ELM633.
The LIN specification has recently been updated
to revision 2.0, incorporating several improvements.
The ELM633 has been updated to be compatible
with this new specification, as well as the previous
ones.
Low power CMOS design
Crystal controlled for accuracy
Standard ASCII character output
Special power-on monitor mode
Permanently set to a 19200bps LIN rate
High speed (57600 baud) RS232 interface
Works with LIN1.x and LIN2.0
2
3
XT1
XT2
6
Timing
Formatting
and
Control
LIN
Interface
LIN
RS232Tx
7
3.58MHz
RS232
Interface
5
4
RS232Rx
Rxmode
LIN logic probes
Diagnostic PC interfaces
Instruction triggered (breakpoint) devices
Educational or training devices
ELM633
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Pin Descriptions
2 of 11
All rights reserved. Copyright 2003, 2004 Elm Electronics.
Every effort is made to verify the accuracy of information provided in this document, but no representation or warranty can be
given and no liability assumed by Elm Electronics with respect to the accuracy and/or use of any products or information
described in this document. Elm Electronics will not be responsible for any patent infringements arising from the use of these
products or information, and does not authorize or warrant the use of any Elm Electronics product in life support devices and/or
systems. Elm Electronics reserves the right to make changes to the device(s) described in this document in order to improve
reliability, function, or design.
V
DD
(pin 1)
This pin is the positive supply pin, and should
always be the most positive point in the circuit.
Internal circuitry connected to this pin is used to
provide power on reset of the microprocessor, so an
external reset signal is not required. Refer to the
Electrical Characteristics section for further
information.
XT1 (pin 2) and XT2 (pin 3)
A 3.579545MHz NTSC television colourburst crystal
is connected between these two pins. Crystal
loading capacitors (typically 27pF) will also be
connected from each of these pins to the circuit
common (Vss).
Rxmode (pin 4)
This input is used to control the inverting of the
signal at the RS232Rx input (pin 5), allowing some
flexibility as to how the RS232 is connected to it.
Many experimenters will prefer to use only a single
resistor between the RS232 interface and pin 5 to
minimize costs. In that case, pin 4 need only be tied
to common (V
SS
), and the internal logic will invert
the polarity of the signal for you.
Other users may prefer to use one of the standard
(inverting) interface circuits such as the MAX232
series, or the SN75189/MC1489 type of IC. In these
cases, the internal inversion is not required, and
should be disabled by connecting the Rxmode input
to a high level (V
DD
). The interface IC can then be
directly connected to the RS232Rx input (pin 5).
RS232Rx (pin 5)
A computer's RS232 transmit signal is connected to
this pin, either through a resistor or through an
interface IC, as discussed under Rxmode (pin 4).
Refer to the Example Applications section for some
typical connections.
A special power-on monitoring mode is entered if
this input is found to be at an active level (as
determined by pin 4) for the entire startup period. In
this mode, the ELM633 will display the ID string, but
instead of issuing a prompt character, it will
immediately execute an AT MA command, reporting
on all LIN bus activity.
RS232Tx (pin 6)
This is the RS232 transmit or data output pin. While
at rest (no data is being sent) this pin will output a
high level (V
DD
), which is compatible with most
interface ICs. It has sufficient current drive to allow
interfacing using only a transistor (if desired).
LIN (pin 7)
This is the active high LIN signal input. The signal
from the LIN bus is inverted and buffered, then
presented to this pin. Note that this input is limited to
voltages from V
SS
to V
DD
, so it can not be directly
connected to the LIN bus. (See the Example
Applications section for a typical interface circuit.)
V
SS
(pin 8)
Circuit common is connected to this pin. This is the
most negative point in the circuit.
ELM633DSB
Ordering Information
These integrated circuits are available in either the 300 mil plastic DIP format, or in the 208 mil SOIC surface mount
type of package. To order, add the appropriate suffix to the part number:
300 mil Plastic DIP...................................ELM633P
208 mil SOIC........................................ ELM633SM
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
ELM633
Electrical Characteristics
Absolute Maximum Ratings
Storage Temperature....................... -65C to +150C
Ambient Temperature with
Power Applied....................................-40C to +85C
Voltage on V
DD
with respect to V
SS
............ 0 to +7.0V
Voltage on any other pin with
respect to V
SS
........................... -0.6V to (V
DD
+ 0.6V)
Note:
Stresses beyond those listed here will likely damage
the device. These values are given as a design
guideline only, and the ability to operate to these
levels is neither inferred nor recommended.
3 of 11
Notes:
1. This integrated circuit is produced with a Microchip Technology Inc.'s PIC12C5XX as the core embedded
microcontroller. For further device specifications, and possibly clarification of those given, please refer to the
appropriate Microchip documentation (available at http://www.microchip.com/).
2. This spec must be met in order to ensure that a correct power on reset occurs. It is quite easily achieved
using most common types of supplies, but may be violated if one uses a slowly varying supply voltage, as
may be obtained through direct connection to solar cells, or some charge pump circuits.
3. This specification represents the current flowing through the internal protection diodes when the voltage
connected to the RS232Rx input (through a current limiting resistance) is greater than V
DD
or less than V
SS
.
Currents quoted are the maximum that should be allowed to flow continuously.
4. Nominal data transfer rate when the recommended 3.58MHz crystal is used as the frequency reference.
Data is transferred to and from the ELM633 with 8 data bits, no parity, and 1 stop bit (8 N 1).
ELM633DSB
All values are for operation at 25C and a 5V supply, unless otherwise noted. For further information, refer to note 1 below.
Characteristic
Minimum
Typical
Maximum
Conditions
Units
Supply voltage, V
DD
4.5
5.0
5.5
V
V
DD
rate of rise
0.05
V/ms
Average supply current, I
DD
0.8
1.4
mA
Input low voltage
V
SS
0.15 x V
DD
V
Input high voltage
V
DD
V
0.85 x V
DD
Output low voltage
0.6
V
Output high voltage
V
V
DD
- 0.7
Current (sink) = 8.7mA
Current (source) = 5.4mA
see note 2
RS232Rx pin input current
mA
see note 3
-0.5
RS232 baud rate
baud
see note 4
57600
+0.5
AT Commands
The ELM633 is controlled with short commands
that all begin with the two characters `AT' (which is
short for ATtention). These two characters serve no
purpose other than to help add validity to the
characters that follow. Modem manufacturers have
used this same technique for years, and it has become
customary to refer to commands that begin with these
characters as `AT Commands'.
The ELM633 accepts several different AT
commands, but only one at a time (it cannot process
multiple commands on one line, as most modems
can). Each is executed only upon receipt of the
terminating carriage return character. Several
commands do not have a visible response (AT D for
example), so completion of those commands will be
4 of 11
ELM633
ELM633DSB
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Communicating with the ELM633
The ELM633 relies on a standard RS232 serial
connection to communicate with the user. The data
rate is not adjustable and is set at 57600 baud, with 8
data bits, no parity bit, 1 stop bit, and no handshaking
(often referred to as 57600 8N1). All responses from
the IC are terminated with a single carriage return
character and, optionally, a linefeed character. Make
sure your software is configured properly for this
connection (and the linefeed mode that you have
chosen). No special software is required to `talk' to the
IC a standard terminal program is all that is needed.
Once it has been properly connected and
powered, the ELM633 will send the message:
ELM633 v2.0
>
In addition to identifying the version of this IC,
receiving this string is a good way to confirm that the
computer connections and terminal software settings
are correct. The `>' character displayed above is the
ELM633's prompt character, which shows that the
device is in its idle state, ready to receive characters
on the RS232 port.
All messages that are sent to the ELM633 must
begin with the character `A' followed by the character
`T', and must be terminated with a carriage return
character. No action is taken commands are not
checked for errors, nor are they acted upon until this
terminating carriage return is received. The one
exception is when a command is interrupted for some
reason, and no carriage return appears. In this case,
an internal timer will automatically abort the incomplete
message after about 15 seconds, and the ELM633 will
print a single question mark to show that the input was
not understood (and was not acted upon).
Messages that are not understood by the ELM633
(syntax errors) will always be signalled by this same
single question mark (`?'). When this occurs, it is
usually due to a spelling mistake, so you often only
need to repeat the input, typing more carefully.
Occasionally, errors occur if the ELM633 is busy
processing LIN messages when an RS232 command
message begins. In these cases, the first character of
the RS232 command message will always be missed
by the IC, so the remaining characters will appear to
be incorrect. You should always interrupt the
monitoring process with a single character (it doesn't
matter which one, as it will be ignored), then wait for
the prompt character (">") to appear before sending
any more. This ensures that the ELM633 is ready to
receive commands.
For convenience, the ELM633 has been designed
to ignore spaces and control characters in the input, so
if you prefer to add spaces, tabs, etc., to improve
readability, then go ahead. Also, the ELM633 is not
case-sensitive, so `ATZ' is equivalent to `atz' and to
`AtZ', which may be helpful for some people.
acknowledged by the printing of the characters `OK'.
Monitoring of the LIN bus can generally begin
without requiring the use of any AT commands, as the
factory default settings should be appropriate for most
situations. Occasionally, however, the user may wish
to customize settings, such as turning the character
echo off, and in these cases, AT commands must be
used.
To perform the desired AT command, simply send
the characters AT followed by the appropriate
characters from the following list. For example, to turn
character echoing off, simply send AT E0 followed by
a return character. To turn it back on, send AT E1.
The following is a summary of the commands that
are recognized by the current version of the ELM633.
5 of 11
ELM633
ELM633DSB
Elm Electronics Circuits for the Hobbyist
< http://www.elmelectronics.com/ >
Remember that they are not case-sensitive, they can
have spaces or tab characters embedded as you wish,
and that for the on/off type commands, the `0'
character is the number zero.
AT Commands (continued)
BR
[ display the Baud Rate ]
This command asks the IC for the LIN baud rate it is
currently operating at. Th ELM633 only supports one
baud rate, so this command will always return with
the response `19200'.
D
[ set all to Defaults ]
This command resets all of the options to their
default values which were set at the last power-up,
or manual reset command. This usually only affects
the echo and linefeed modes, but if the RS232Rx
pin was at an active level during the last reset, the
IC will immediately enter the Monitor All (AT MA)
mode after this command is issued.
E0 and E1
[ Echo off(0) or on(1) ]
These commands control whether or not characters
received on the RS232 port are re-transmitted (or
echoed) back to the host computer. To reduce traffic
on the RS232 bus, users may wish to turn echoing
off by issuing AT E0. The default is E1 (echo on).
I
[ Identify yourself ]
Issuing this command causes the chip to identify
itself, by printing the startup product ID string (which
is currently `ELM633 v2.0'). Software can use this to
determine exactly which integrated circuit it is talking
to, without resorting to resetting the entire IC.
L0 and L1
[ Linefeeds off(0) or on(1) ]
The option of transmitting a linefeed character after
each carriage return character is controlled by these
commands. If an AT L1 is issued, linefeed
generation will be turned on, and for AT L0, it will be
off. Users may wish to have this option on if using a
terminal program, but off if using a custom interface
(as the extra characters serve no real purpose in
such a case). The default setting is L1 (linefeed
characters are sent after every carriage return).
MA
[ Monitor All ]
This command causes the IC to immediately begin
monitoring the LIN bus for messages, displaying all
that it finds. It can be interrupted at any time by
activity on the RS232 receive input.
MR hh
[ Monitor for a Response to hh ]
This is a special version of the AT MA command.
Only identifier/command bytes matching the hex
characters `hh' will be displayed, and all others will be
ignored. This can be useful if trying to track down a
troublesome switch problem, or for triggering another
action on a specific input.
Z
[ reset all ]
This combination causes the chip to perform a
complete reset, as if power was cycled off and then
on again. All settings are returned to their default
values, and if the RS232Rx input is not held at an
active level for the entire reset time, the chip will be
put in the idle state, waiting for characters to arrive
on the RS232 bus. Note that the level at the Rxmode
input is measured again at this time, so the RS232Rx
input may be affected if the level at pin 4 has
changed since the initial power-up.
PDF 
ZIP