ELM329LSM datasheet(14/87 Pages) ELM

14 / 87 page

14 of 87

ELM329L

ELM329L DSA

Elm Electronics – Circuits for the Hobbyist

www.elmelectronics.com

AT Command Descriptions (continued)

is always as set by AT ST), while AT2 is a more

aggressive version of AT1 (the effect is more

noticeable for very slow connections – you may not

see much difference with faster OBD systems). The

J1939 protocol does not support Adaptive Timing – it

uses fixed timeouts as set in the standard.

[ perform an OBD Buffer Dump ]

All messages sent and received by the ELM329

are stored temporarily in a set of twelve memory

storage locations called the OBD Buffer. Occasionally,

it may be useful to see the contents of this buffer,

perhaps to see why a request failed, to see the header

bytes in the last message, or just to learn more of the

structure of OBD messages. You can ask at any time

for the contents of this buffer to be ‘dumped’

(ie printed). When you do, the ELM329 sends a length

byte (representing the length of the current message in

the buffer) followed by the contents of all twelve OBD

buffer locations. For example, here’s one ‘dump’:

>AT BD

0C 00 00 07 E8 03 41 05 42 00 00 00 00

The 0C is the length byte - it tells us that the

following 12 bytes are valid. The actual bytes that have

been sent or received appear after the length. Note

that wakeup (CAN periodic) messages do not use the

buffer as an intermediate step, so you are not able to

see them with AT BD.

[ Bypass the Initialization sequence ]

This command should be used with caution. It

allows the currently selected protocol to be made

active without requiring any sort of initiation or

handshaking to occur. The initiation process is

normally used to validate the protocol, and without it,

results may be difficult to predict. It should not be used

for routine OBD use, and has only been provided to

allow the construction of ECU simulators and training

demonstrators.

BRD hh

[ try Baud Rate Divisor hh ]

This command is used to change the RS232 baud

rate divisor to the hex value provided by hh, while

under computer control. It is not intended for casual

experimenting - if you wish to change the baud rate

from a terminal program, you should use PP 0C.

Since some interface circuits are not able to be

operated at high data rates, the BRD command uses a

sequence of sends and receives to test the interface,

with any failure resulting in a fallback to the previous

baud rate. This allows several baud rates to be tested

and a reliable one chosen for the communications.

The entire process is described in detail in the ‘Using

Higher RS232 Baud Rates’ section, on pages 46 and

47.

If successful, the actual baud rate (in kbps) will be

4000 divided by the divisor (hh).

BRT hh

[ set Baud Rate Timeout to hh ]

This command allows the timeout used for the

Baud Rate handshake (ie. AT BRD) to be varied. The

time delay is given by hh x 5.0 msec, where hh is a

hexadecimal value. The default value for this setting is

0F, providing a 75 msec timeout. Note that a value of

00 does not result in 0 msec -

it provides the

maximum time of 256 x 5.0 msec, or 1.28 seconds.

C0 and C1

[ Control output off* or on ]

These commands are used to set the level at the

Control output (pin 4). The AT C0 command sets it to a

low logic level (0V), while AT C1 sets it to a high level

(5V). After a system reset or wakeup from low power

mode (unless PP 0F bit 0 = ‘1’), the Control output will

be reset to a low level.

[is there CAN Activity at pin 11?]

This command is used to determine if there is a

CAN signal present at pin 11 (the CAN Monitor pin). If

there is, the response will be the letter ‘Y’ (for yes),

while if there is no signal, the response will be the

letter ‘N’, for no. If there has been no signal detected

since the last reset, the output will be a dash (‘-’).

CAF0 and CAF1

[ CAN Auto Formatting off or on ]

These commands determine whether the ELM329

assists you with the formatting of the CAN data that is

sent and received. With CAN Automatic Formatting

enabled (CAF1), the IC will automatically generate the

formatting (PCI) bytes for you when sending, and will

remove them when receiving. This means that you can

continue to issue OBD requests (01 00, etc.), without

regard to the extra bytes that some CAN systems

require. Also, with formatting on, any extra (unused)

data bytes that are received in the frame will be

removed, and any messages with invalid PCI bytes will

ELM329LSM bảng dữ liệu(PDF) 14 Page - ELM Electronics

ELM329LSM bảng dữ liệu(HTML) 14 Page - ELM Electronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87

bảng dữ liệu tải về

Link URL