ELM327P datasheet(14/76 Pages) ELM

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ELM327

ELM327DSH

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CRA

[reset the CAN Rx Addr]

The AT CRA command is used to restore the CAN

receive filters to their default values. Note that it does

not have any arguments (ie no data).

CRA hhh

[set the CAN Rx Addr to hhh]

Setting the CAN masks and filters can be difficult

at times, so if you only want to receive information

from one address (ie. one CAN ID), then this

command may be very welcome. For example, if you

only want to see information from 7E8, simply send AT

CRA 7E8, and the ELM327 will make the necessary

adjustments to both the mask and the filter for you.

Note that this command restricts viewing to only

the one ID - to allow reception of a range of IDs, you

must set the mask and filter independently (described

in detail on page 41). To reverse the changes made by

the CRA command, simply send AT CRA or AT AR.

CRA hhhhhhhh [set the CAN Rx Addr to hhhhhhhh]

This command is identical to the previous one,

except that it is used to set 29 bit CAN IDs, instead of

11. Sending either AT CRA or AT AR will also reverse

the changes made by this command.

[ show the CAN Status counts ]

The CAN protocol requires that statistics be kept

regarding the number of transmit and receive errors

detected. If there should be a significant number of

errors (due to a hardware or software problem), the

device will go off-line in order to not affect other data

on the bus. The AT CS command lets you see both

the transmitter (Tx) and the receiver (Rx) error counts,

in hexadecimal. If the transmitter should be off (count

>FF), you will see ‘OFF’ rather than a specific count.

CSM0 and CSM1

[ CAN Silent Monitoring off or on ]

The ELM327 was designed to be completely silent

while monitoring a CAN bus. Because of this, it is able

to report exactly what it sees, without colouring the

information in any way. Occasionally (when bench

testing, or when connecting to a dedicated CAN port),

it may be preferred that the ELM327 does not operate

silently (ie generates ACK bits, etc.), and this is what

the CSM command is for. CSM1 turns it on, CSM0

turns it off, and the default value is determined by

PP 21. Be careful when experimenting with this. If you

should choose the wrong baud rate then monitor the

CAN bus with the silent monitoring off, you will disturb

the flow of data. Always keep the silent monitoring on

until you are certain that you have chosen the correct

baud rate.

CV dddd

[ Calibrate the Voltage to dd.dd volts ]

The voltage reading that the ELM327 shows for an

AT RV request can be calibrated with this command.

The argument (‘dddd’) must always be provided as 4

digits, with no decimal point (it assumes that the

decimal place is between the second and the third

digits).

To use this feature, simply use an accurate meter

to read the actual input voltage, then use the CV

command to change the internal calibration (scaling)

factor. For example, if the ELM327 shows the voltage

as 12.2V while you measure 11.99 volts, then send

AT CV 1199 and the ELM327 will recalibrate itself for

that voltage (it will actually read 12.0V due to digit

roundoff). See page 27 for some more information on

how to read voltages and perform the calibration.

CV 0000

[ restore the factory Calibration Value ]

If you are experimenting with the CV dddd

command but do not have an accurate voltmeter as a

reference, you may soon get into trouble. If this

happens, you can always send AT CV 0000 to restore

the ELM327 to the original calibration value.

[ set all to Defaults ]

This command is used to set the options to their

default (or factory) settings, as when power is first

applied. The last stored protocol will be retrieved from

memory, and will become the current setting (possibly

closing other protocols that are active). Any settings

that the user had made for custom headers, filters, or

masks will be restored to their default values, and all

timer settings will also be restored to their defaults.

D0 and D1

[ display of DLC off or on ]

Standard CAN (ISO 15765-4) OBD requires that

all messages have 8 data bytes, so displaying the

number of data bytes (the DLC) is not normally very

useful. When experimenting with other protocols,

however, it may be useful to be able to see what the

data lengths are. The D0 and D1 commands control

AT Command Descriptions (continued)

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