ELM320DSD 데이터 시트보기 (PDF) - Elm Electronics

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ELM320DSD

OBD (PWM) to RS232 Interpreter

Elm Electronics 

ELM320

AT Commands (continued)

I

[ Identify yourself ]

Issuing this command causes the chip to identify

itself, by printing the startup product ID string (this is

currently ‘ELM320 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) ]

Whether the ELM320 transmits a linefeed character

after each carriage return character is controlled by

this option. If an ATL1 is issued, linefeed generation

will be turned on, and for ATL0, 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 transmitted will only serve to slow

the vehicle polling down). The default setting is L1

(linefeeds on)

MA

[ Monitor All messages ]

Using this command places the ELM320 into a bus

monitoring mode, in which it displays all messages

as it sees them on the OBD bus. This continues

indefinitely until stopped by activity on the RS232

input. To stop the monitoring, one should send any

single character then wait for the ELM320 to respond

with a prompt character (‘>’). Waiting for the prompt

is necessary as the response time is unpredictable,

varying depending on the IC was doing when

interrupted. If for instance it is in the middle of

printing a line, it will first complete the line then

return to the command state, issuing the prompt

character. If it were simply waiting for input, it would

return immediately. The character which stops the

monitoring will always be discarded, and will not

affect subsequent commands.

MR hh

[ Monitor for Receiver hh ]

This command also places the IC in a bus monitoring

mode, displaying only messages that were sent to

the hex address given by hh (i.e. messages which

are found to have that value in their second byte).

Any RS232 activity (single character) aborts the

monitoring, as with the MA command.

MT hh

[ Monitor for Transmitter hh ]

Another monitoring command, which displays only

messages sent by Transmitter address hh. As with

the MA and MR monitoring modes, any RS232

activity (single character) aborts the monitoring.

PD

[ send Packed Data ]

This option is for those that are building a computer

interface and want the fastest data transfer rate

possible while still operating at 9600 baud. When

selected, responses from the vehicle will be

formatted as an initial length byte followed by the

actual response bytes from the vehicle, with no

trailing carriage returns or linefeed characters. The

data will not be altered in any way, except for the

conversion to standard RS232 bytes.

Note that the length byte only represents the total

number of data bytes following, and does not include

itself. Also, if there was a data (checksum) error, the

length byte will have its most significant bit set, so

the user should always check first to see if the length

is greater than 127. (The other 7 bits still provide a

valid byte count if there is an error, so one need only

ignore the msb, or subtract 128 from the value.)

A ‘NO DATA’ response has no data bytes, but still

sends a length byte with value ‘0’.

R0 and R1

[ Responses off (0) or on(1) ]

These commands control the ELM320’s automatic

display of responses. If responses have been turned

off, the IC will not wait for anything to be returned

from the vehicle after sending a request, and will

return immediately to waiting for RS232 commands.

This is useful if sending commands blindly when

using the IC for a non-OBD network application, or

simulating an ECU, in a basic learning environment.

It is not recommended that this option normally be

used, however, as the vehicle may have difficulty if it

is expecting an acknowledgement byte and never

receives one. The default is R1 (responses on).

SH xx yy zz

[ Set the Header to xx yy zz ]

This command allows the user to control the values

that are sent as the three header bytes in the

message. The value of hex digits xx will be used for

the first or priority/type byte, yy will be used for the

second or target byte, and zz will be used for the

third or source byte. These remain in effect until set

again, or until restored to the default values with the

AT D, or AT Z commands. The default header values

ELM320DSD

Elm Electronics – Circuits for the Hobbyist

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