ELM329 データシートの表示（PDF） - Elm Electronics

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ELM329

CAN Interpreter

Elm Electronics 

ELM329

AT Command Descriptions (continued)

formats the J1939 ID (ie Header) bits in such a way as

to isolate the priority bits and group all the PGN

information, while keeping the source address byte

separate. If you prefer to see the ID information as four

separate bytes (which a lot of the J1939 software

seems to do), then simply turn off the formatting with

JHF0. The CAF0 command has the same effect (and

overrides the JHF setting), but also affects other

formatting. The default setting is JHF1.

JS

[ enables the J1939 SAE data format ]

The AT JS command disables the automatic byte

reordering that the JE command performs for you. If

you wish to send data bytes to the J1939 vehicle

without any manipulation of the byte order, then select

JS formatting.

Using the above example for engine temperature

(PGN 00FEEE) with the data format set to JS, you

must send the bytes to the ELM329 as EE FE 00 (this

is also known as little-endian byte ordering).

The JS type of data formatting is off by default.

JTM1

[ J1939 Timer Multiplier to 1 ]

This command sets the J1939 AT ST time

multiplier to 1, reversing any changes made by JTM5.

JTM1 is the default setting. It has no effect for non-

J1939 protocols.

JTM5

[ J1939 Timer Multiplier to 5 ]

When using a J1939 protocol, it is occasionally

useful to be able to set the AT ST time to values

longer than one second. The JTM5 command will

multiply the AT ST setting by a factor of 5, in order to

provide longer times for the J1939 protocols (only). By

default, this multiplier is off.

L0 and L1

[ Linefeeds off or on ]

This option controls the sending of linefeed

characters after each carriage return character. For

AT L1, linefeeds will be generated after every carriage

return character, and for AT L0, they will be off. Users

will generally wish to have this option on if using a

terminal program, but off if using a custom computer

interface (as the extra characters transmitted will only

serve to slow the communications down). The default

setting is determined by the voltage at pin 7 during

power on (or reset). If the level is high, then linefeeds

are on by default; otherwise they will be off.

LP

[ go to the Low Power mode ]

This command causes the ELM329 to shut off all

but ‘essential services’ in order to reduce the power

consumption to a minimum. The ELM329 will respond

with an ‘OK’ (but no carriage return) and then, one

second later, will change the state of the PwrCtrl

outputs (pins 14 & 16) and will enter the low power

(standby) mode. The IC can be brought back to normal

operation with an RS232 input, CAN activity, or a

rising edge at the IgnMon (pin 15) input, in addition to

the usual methods of resetting the IC (power off then

on, a low on pin 1, or a brownout). See the ‘Low Power

Mode’ section (page 57) for more information.

M0 and M1

[ Memory off or on ]

The ELM329 has internal ‘non-volatile’ memory

that is capable of remembering the last protocol used,

even after the power is turned off. This can be

convenient if the IC is often used for one particular

protocol, as that will be the first one attempted when

next powered on. To enable this memory function, it is

necessary to either use an AT command to select the

M1 option, or to have chosen ‘memory on’ as the

default power on mode (by connecting pin 5 of the

ELM329 to a high logic level).

When the memory function is enabled, each time

that the ELM329 finds a valid OBD protocol, that

protocol will be memorized (stored) and will become

the new default. If the memory function is not enabled,

protocols found during a session will not be

memorized, and the ELM329 will always start at power

up using the same (last saved) protocol.

If the ELM329 is to be used in an environment

where the protocol is constantly changing, it would

likely be best to turn the memory function off, and

issue an AT SP 0 command once. The SP 0 command

tells the ELM329 to start in an 'Automatic' protocol

search mode, which is the most useful for an unknown

environment. ICs come from the factory set to this

mode. If, however, you have only one vehicle that you

regularly connect to, storing that vehicle’s protocol as

the default would make the most sense.

The default setting for the memory function is

determined by the voltage level at pin 5 during power

up (or system reset). If it is connected to a high level

(VDD), then the memory function will be on by default.

If pin 5 is connected to a low level, the memory saving

will be off by default.

ELM329DSB

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

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