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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  
Reading the Battery Voltage  
Before learning the OBD Commands, we will show  
an example of how to use an AT Command. We will  
assume that you have built (or purchased) a circuit  
which is similar to that of Figure 9 in the Example  
Applications section (page 67). This circuit provides a  
connection to read the vehicle’s battery voltage, which  
many will find very useful.  
the CV value, as the ELM329 knows that it should be  
between the second and the third digits.  
At this point, the internal calibration values have  
been changed (ie. written to EEPROM), and the  
ELM329 now knows that the voltage at the input is  
actually 12.47V. To verify that the changes have taken  
place, simply read the voltage again:  
If you look in the AT Command list, you will see  
there is one command that is listed as RV [Read the  
input Voltage]. This is the command which you will  
need to use. First, be sure that the prompt character is  
shown (that is the ‘>’ character), then simply enter ‘AT’  
followed by RV, and press return (or enter):  
>AT RV  
12.5V  
The ELM329 always rounds off the measurement  
to one decimal place, so the 12.47V actually appears  
as 12.5V (but the second decimal place is maintained  
internally for accuracy and is used in the calculations).  
The ELM329 may be calibrated with any reference  
voltage that you have available, but note that the CV  
command always expects to receive four characters  
representing the voltage at the input. If you had used a  
9V battery for your reference, and it is actually 9.32V,  
then you must add a leading zero to the actual voltage  
when calibrating the IC:  
>AT RV  
Note that we used upper case characters for this  
request, but it was not required, as the ELM329 will  
accept upper case (AT RV) as well as lower case  
(at rv) or any combination of these (At rV). It does not  
matter if you insert space characters (‘ ’) within the  
message either, as they are ignored by the ELM329.  
A typical response to this command will show a  
voltage reading, followed by another prompt character:  
>AT CV 0932  
OK  
12.6V  
>
If you should get into trouble with this command  
(for example, if you set calibration values to something  
arbitrary and do not have a voltmeter on hand to  
provide accurate values), you can restore the settings  
to the original (factory) values with the CV 0000  
command. Simply send:  
The accuracy of this reading depends on several  
factors. As shipped from the factory, the ELM329  
voltage reading circuitry will typically be accurate to  
about 2%. For many, this is all that is needed. Some  
people may want to calibrate the circuitry for more  
accurate readings, however, so we have provided a  
special ‘Calibrate Voltage’ command for this.  
>AT CV 0000  
OK  
To change the internal calibration constants, you  
will need to know the actual battery voltage to more  
accuracy than the ELM329 shows. Many quality digital  
multimeters can do this, but you should verify the  
accuracy before making a change.  
Let us assume that you have connected your  
accurate multimeter, and you find that it reads 12.47V.  
The ELM329 is a little high at 12.6V, and you would  
like it to read the same as your meter. Simply calibrate  
the ELM329 to the measured voltage using the CV  
command:  
The other AT Commands are used in the same  
manner. Simply type the letters A and T, then follow  
with the command you want to send and any  
arguments that are required. Then press return (or  
enter, depending on your keyboard). Remember - you  
can always insert space characters as often as you  
wish if it improves the readability for you, as they are  
ignored by the ELM329.  
>AT CV 1247  
OK  
Note that you should not provide a decimal point in  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
25 of 76  
www.elmelectronics.com