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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  
ISO 15765-4 Message Types  
If you are going to be adjusting the header values,  
you will likely be experimenting with the data bytes as  
well, so should have some knowledge of the message  
structures. The ISO 15765-4 standard defines several  
message types that may be used with diagnostic  
systems. Currently, there are four of them:  
Frame’. The length (014) was actually extracted from  
that line by the ELM329 and printed on the first line as  
shown. Following the First Frame line are two  
Consecutive Frames (that begin with 1: and 2:). To  
learn more details of the exact formatting, you may  
want to send a request such as the one above, then  
repeat the same request with the headers enabled (AT  
H1). This will show the PCI bytes that are actually  
used to send these components of the total message.  
The Flow Control frame is one that you do not  
normally have to deal with. When a First Frame  
message is sent as part of a reply, the ELM329 must  
tell the sender some technical things (such as how  
long to delay between Consecutive Frames, etc.) and  
does so by replying immediately with a Flow Control  
message. These are predefined by the ISO 15765-4  
standard, so can be automatically inserted for you. If  
you wish to generate custom Flow Control messages,  
then refer to the ‘Altering Flow Control Messages’  
section, on page 54.  
SF - the Single Frame  
FF - the First Frame (of a multiframe message)  
CF - the Consecutive Frame ( “ “ )  
FC - the Flow Control frame  
The Single Frame message contains storage for  
up to seven data bytes in addition to what is known as  
a PCI (Protocol Control Information) byte. The PCI  
byte is always the first of the data bytes, and tells how  
many data bytes are to follow. If the CAN Auto  
Formatting option is on (CAF1) then the ELM329 will  
create this byte for you when sending, and remove it  
for you when receiving. (If the headers are enabled,  
you will see it in the responses.)  
If you turn the Auto Formatting off (with CAF0), it  
is expected that you will provide all of the data bytes to  
be sent. For diagnostics systems, this means the PCI  
byte and the data bytes. The ELM329 will not modify  
your data in any way, except to add extra padding  
bytes for you, to ensure that you always send as many  
data bytes as are required (eight for ISO 15765).  
A First Frame message is used to say that a multi-  
frame message is about to be sent, and tells the  
receiver just how many data bytes to expect. The  
length descriptor is limited to 12 bits, so a maximum of  
4095 bytes can be received at once using this method.  
Consecutive Frame messages are sent after the  
First Frame message to provide the remainder of the  
data. Each Consecutive Frame message includes a  
single hex digit ‘sequence number’ that is used to  
determine the order when reassembling the data. It is  
expected that if a message were corrupted and resent,  
it could be out of order by a few packets, but not by  
more than 16, so the single digit is normally more than  
adequate. As an example, the serial number for a  
vehicle is a multiframe response:  
While you will not generally see Flow Control  
frames while querying a vehicle, you may see them if  
you are monitoring data requests. If detected, the  
ELM329 will display such a line with ‘FC: ’ before the  
data, to help you with decoding the information.  
There is a final type of message that is  
occasionally reported, but is not supported by the OBD  
diagnostics standard. The (Bosch) CAN standard  
allows for the transmission of a data request without  
sending any data in the requesting message. To  
ensure that the message is seen as such, the sender  
also sets a special flag in the message (the RTR bit),  
which is seen at each receiver. The ELM329 always  
looks for this flag, or for zero data bytes, and may  
report to you that a Remote Transmission Request  
was detected while monitoring. This is shown by the  
characters RTR where data would normally appear,  
but only if the CAN Auto Formatting is off, or headers  
are enabled. Often, when monitoring a CAN system  
with an incorrect baud rate chosen, RTRs may be  
seen.  
>0902  
014  
0: 49 02 01 31 44 34  
1: 47 50 30 30 52 35 35  
2: 42 31 32 33 34 35 36  
The line that begins with 0: is called the ‘First  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
36 of 76  
www.elmelectronics.com