65 of 83ELM329DSC Elm Electronics – Circuits for the Hobbyist
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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).
06 OBD Source (Tester) Address. Not used for J1939 protocols. F1 R
07 ILast Protocol to try during automatic searches 09
PP
Description Values Default Type
01 Printing of header bytes (AT H default setting) D
03 NO DATA timeout time (AT ST default setting)
setting = value x 4.096 msec
00 to FF 19
(102 msec)
D
09 Character echo (AT E default setting) R
0A Linefeed Character 0A R
00 Perform AT MA immediately after powerup or reset FF
(OFF)
R
00
(ON)
00 = ON
FF = OFF
00 to FF
01 to 0F
00 to FF
FF
(OFF)
00 to 02 01 D04 Default Adaptive Timing mode (AT AT setting)
00 = ON
FF = OFF
00 = ON
FF = OFF
Programmable Parameter Summary
The following pages provide a list of the currently
available Programmable Parameters. If a PP number
is not shown in this table, then it does not currently
have a function and it will not affect the operation of
the ELM329.
All values shown are hexadecimal - the ELM329
does not recognize decimal numbers. Note that the
‘Type’ column indicates when any changes will take
effect. The four possible values are as shown to the
right (I, D, R or P).
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
(AT Z, AT WS, MCLR or power off/on)
P - needs a Power off/on type reset
(AT Z, MCLR, or power off/on)
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