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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  
Altering Flow Control Messages  
A CAN message provides for only eight data bytes  
per frame of data. Of course, there are many cases  
where the data which needs to be sent is longer than 8  
bytes, and ISO 15765 has made provision for this by  
allowing data to be separated into segments, then  
recombined at the receiver.  
To send one of these multi-line messages, the  
transmitter in a CAN system will send a ‘First Frame’  
message, and then wait for a reply from the receiver.  
This reply, called a ‘Flow Control’ message contains  
information concerning acceptable message timing,  
etc., and is required to be sent before the transmitter  
will send any more data. For ISO 15765-4, the type of  
response is well defined, and never changes. The  
ELM329 will automatically send this ISO 15765-4 Flow  
Control response for you as long as the CAN Flow  
Control option is enabled (CFC1), which it is by  
default.  
and then you can set the mode:  
>AT FC SM 1  
OK  
From this point on, every First Frame message  
received will be responded to with the custom  
message that you have defined (7E8 00 11 22 in this  
example). Note that the number of bits in the flow  
control header does not have to match the number in  
the active protocol (you may define a 29 bit header for  
11 bit systems, etc.)  
The third mode currently supported allows the  
user to set the data bytes which are to be sent. The ID  
bits (header bytes) in this mode are set to those which  
were received in the First Frame message, without  
change. To use this mode, first define your data bytes,  
then activate the mode:  
The ELM329 allows you to customize how it  
responds when it needs to send a Flow Control  
message, by changing the Flow Control ‘modes’. You  
can leave it as a fully automatic response (mode 0),  
can provide only the data bytes that you want sent  
(mode 2) or can define both the header (ID bits) and  
the data bytes (mode 1).  
The default Flow Control mode is number ‘0’. At  
any time while you are experimenting, if you should  
wish to restore the automatic Flow Control responses  
(for ISO 15765-4), simply change the mode to 0:  
>AT FC SD 30 00 00  
OK  
>AT FC SM 2  
OK  
For most people, there will be little need to  
manipulate these ‘Flow Control’ messages, as the  
defaults are designed to work with the CAN OBD  
standards. If you wish to experiment, these special AT  
commands offer that control for you.  
The following chart summarizes the currently  
supported flow control modes:  
>AT FC SM 0  
OK  
FC  
Mode  
ELM329  
Provides  
User  
Provides  
This will immediately restore the responses to their  
default settings.  
ID Bits &  
Data Bytes  
Mode 1 has been provided for those that need  
complete control over their Flow Control messages. To  
use it, simply define the CAN ID (header) and data  
bytes that you require to be sent in response to a First  
Frame message. Note that if you try to set the mode  
before defining these values, you will get an error:  
0
1
2
no values  
ID Bits &  
Data Bytes  
no values  
ID Bits  
Data Bytes  
>AT FC SM 1  
?
Flow Control Modes  
You must set the headers and data first:  
Note that the ELM329 will only send Flow Control  
messages if the current data format is ISO 15765-4.  
>AT FC SH 7E8  
OK  
>AT FC SD 30 00 00  
OK  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
www.elmelectronics.com  
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