ELM329
Programmable Parameters (continued)
command, so if you change its value, you may not be
able to undo your change. In this case, your only
recourse may be to force all of the PPs off with a
hardware trick.
When the ELM329 first powers up, it looks for a
jumper between pin 28 (the OBD Tx LED output) and
circuit common (VSS). If a jumper is in place, it will turn
off all of the PPs for you, restoring the IC to the factory
defaults. To use this feature, simply connect a jumper
to circuit common (which appears in numerous places
- pins 8 or 19 of the ELM329, pin 5 of the RS232
connector, one end of most capacitors, or at the OBD
connector), then hold the other end of the jumper to
pin 28 while turning the power on. When you see the
RS232 Rx LED begin to flash quickly, remove the
jumper – the PPs are off.
This feature should only be used when you get
into trouble too deeply, and it’s your only choice (since
putting a jumper into a live circuit might cause damage
if you put it in the wrong place).
Programmable Parameter Summary
The following pages provide a list of the currently
available Programmable Parameters (the currently
unimplemented ones are not shown here). All values
are in hexadecimal - the ELM329 does not accept
decimal numbers.
I - the effect is Immediate,
D - takes effect after Defaults are restored
(AT D, AT Z, AT WS, MCLR or power off/on)
R - takes effect after a Reset
Note that the ‘Type’ column indicates when any
changes will take effect. The four possible values are
as shown to the right:
(AT Z, AT WS, MCLR or power off/on)
P - needs a Power off/on type reset
(AT Z, MCLR, or power off/on)
PP
Description
Values
Default
Type
00
Perform AT MA immediately after powerup or reset
00 = ON
FF = OFF
FF
R
(OFF)
01
03
04
06
07
09
0A
Printing of header bytes (AT H default setting)
00 = ON
FF = OFF
FF
D
D
D
R
I
(OFF)
NO DATA timeout time (AT ST default setting)
setting = value x 4.096 msec
00 to FF
00 to 02
00 to FF
01 to 0F
19
(102 msec)
Default Adaptive Timing mode (AT AT setting)
OBD Source (Tester) Address. Not used for J1939 protocols.
Last Protocol to try during automatic searches
Character echo (AT E default setting)
01
F1
0F
00 = ON
FF = OFF
00
R
R
(ON)
Linefeed Character
00 to FF
0A
ELM329DSB
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