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ELM329P 参数 Datasheet PDF下载

ELM329P图片预览
型号: ELM329P
PDF下载: 下载PDF文件 查看货源
内容描述: CAN解释 [CAN Interpreter]
分类和应用:
文件页数/大小: 76 页 / 353 K
品牌: ELM [ ELM ELECTRONICS ]
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ELM329  
Periodic (Wakeup) Messages  
Some applications require that there be periodic  
messages sent by the test equipment (scan tool) in  
order to maintain a connection. If these messages do  
not arrive in a timely fashion, the ECU will close the  
connection and go into a low power ‘sleep’ mode. In  
order to stop the ECU from going to sleep, you may  
need to send what we term as ‘wakeup’ messages.  
Some texts also refer to these as CAN periodic  
messages.  
The ELM329 does not send wakeup messages by  
default - you must enable the sending of them (and  
you may also need to define what you wish to have  
sent).  
There are a few conditions that need to be met  
before the ELM329 will send periodic messages. First,  
you must be selected for a defined CAN protocol (ie  
not set to protocol 0), and the protocol must be in the  
‘normal’ mode of operation. That is, it must be in the  
mode where you send and receive messages, not in  
one of the ‘monitoring’ modes (as entered with AT MA,  
DM1, or MP). In addition, either Wakeup Mode 1 or 2  
must be chosen, either by command (see below) or by  
PP 23.  
>AT WD 01 3E  
OK  
with the 11 bit example from above, will result in the  
following being sent by the ELM329:  
7DF 01 3E  
The difference here is that the data length is no  
longer 8 bytes - it has been set to two, as that is the  
number of data bytes that you provided (so if you want  
the message to use 8 bytes, you need to provide 8  
bytes).  
Once you have the wakeup header and data set  
as you want them, you are ready to begin sending the  
messages. To do this, simply set the Wakeup Mode:  
>AT WM 1  
OK  
Enabling Wakeup Mode 1 results in the wakeup  
messages being sent at a constant rate, no matter  
what information is going back and forth on the CAN  
bus. Wakeup Mode 2 is the other option - it causes the  
wakeup timer to be reset after every message is sent  
by the ELM329, and will only insert a wakeup  
message if the normal data messages are not being  
sent often enough.  
Once enabled, the ELM329 will send the following  
message by default:  
7DF 01 3E 00 00 00 00 00 00  
The time interval between the wakeup messages  
can be adjusted in 20.48 msec increments using the  
AT SW command. Simply provide the setting that you  
require as two hex digits - for example, a setting of:  
Note that this default wakeup message uses an 11  
bit ID, and sends 8 data bytes. This message will be  
sent, even if the current protocol uses a 29 bit ID. If  
you wish to send a 29 bit ID, then you will need to  
define one with the Wakeup Header command:  
>AT SW 92  
OK  
>AT WH 18 DB 33 F1  
OK  
will result in a timer setting of about 3 seconds (92 hex  
is 146 decimal, giving 2.99 seconds). The default timer  
setting is 62 (98 decimal) or 2.0 seconds.  
To turn off the wakeup messages at any time,  
select Wakeup Mode 0:  
and from that point on, the wakeup message will be  
sent with the 29 bit header (the ELM329 always uses  
the last ID that was defined using AT WH). Of course,  
the above header is only an example - you may define  
any values that you wish for the ID bits.  
Setting the actual content of the Wakeup Message  
is accomplished with either the Wakeup Data (AT WD)  
or the Wakeup Message (AT WM) commands. They  
are exactly the same (we’ve kept the WM that the  
ELM327 used, and the WD is new). The ELM329 does  
not format the data provided in any way, and it does  
not pad it out to 8 bytes. Whatever you provide will be  
used exactly as you present it. For example, sending:  
>AT WM 0  
OK  
The sending of wakeup messages will also be  
cancelled if you enter into one of the monitoring modes  
by using the AT MA, DM1 or MP commands.  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
www.elmelectronics.com  
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