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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  
Microprocessor Interfaces  
A very common question that we receive is ‘Can I  
connect the ELM329 directly to my own circuit, or must  
I use the RS232 interface shown?’ Certainly you may  
connect directly to our ICs, and you do not need to use  
an RS232 interface. There are a few items to consider,  
however.  
The ELM329 is actually a microprocessor that  
contains a standard UART type interface, connected to  
the RS232 Tx and Rx pins. The logic type is CMOS,  
and this is compatible with virtually all 5V TTL and  
CMOS circuits, so you should be able to connect  
directly to these pins provided that the two devices  
share the same power supply (5V), and that they are  
not physically more than about 10 to 20 inches apart  
(CMOS circuits are subject to latchup from induced  
currents, which may be a problem if you have long  
leads).  
The normal (idle) levels of the ELM329 transmit  
and receive pins are at the VDD (5V) level. Most  
microprocessors and RS232 interface ICs expect that  
to be the idle level, but you should verify it for your  
microprocessor before connecting to the ELM329. The  
connections are straightforward - transmit connects to  
receive, and receive connects to transmit, as shown  
below. Don’t forget to set both devices to the same  
baud rate.  
the low power feature off). The interface consists of  
two pins - an input an an output. The input is called  
‘request to send’ (RTS), and it is used to interrupt the  
ELM329, just the same as tapping a key on the  
keyboard when using a terminal program. The output  
pin (‘Busy’) is used by the ELM329 to tell your system  
that it is processing data.  
To use the handshaking feature, set one of your  
port pins to normally provide a high output, and  
connect it to the RTS input (pin 15). Use another port  
pin as an input to monitor the ELM329 Busy output  
(pin 16). When you want to send a command, simply  
check the Busy output first. If it is at a high logic level,  
then either wait for it to go low, or if you need to  
interrupt the IC, then bring the RTS line low and wait  
for the Busy line to go low. (You might want to  
consider using an edge triggered interrupt on the Busy  
output, if one is available). When Busy does go low,  
restore your RTS line to a high level, and then send  
your command to the ELM329. No need to worry  
about the ELM329 becoming busy again after you  
raise the RTS line at this point – once Busy goes low,  
the ELM329 will wait (indefinitely) for your command.  
If you do not use the RTS input on the ELM329, it  
must be connected to a high logic level, as shown  
below.  
The ELM329 also provides a hand-shaking feature  
that may simplify the flow of data for you (if you turn  
+5V  
your microprocessor  
+5V  
Tx  
Rx  
+5V  
+5V  
28  
27  
26  
25  
24  
23  
22  
21  
20  
19  
10  
18  
17  
16  
15  
The ELM329 and your  
microprocessor must  
use the same 5V supply  
Rx Tx Busy RTS  
329  
1
2
3
4
5
6
7
8
9
11  
12  
13  
14  
X1  
4.00MHz  
C3  
27pF  
C4  
27pF  
ELM329DSB  
Elm Electronics – Circuits for the Hobbyist  
67 of 76  
www.elmelectronics.com