612699
76
Zoom out
Zoom in
Previous page
1/94
Next page
A very common question that we receive is ‘Can I
connect the ELM327 directly to my own circuit, or must
I use the interface shown?’ Certainly you may connect
directly to our ICs, and you do not need to use an
RS232 or USB interface. There are a few items to
consider, however.
The ELM327 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 latch-up from induced
currents, which may be a problem if you have long
leads).
The normal (idle) levels of the ELM327 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 ELM327. 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 ELM327 also provides a hand-shaking feature
that may simplify the flow of data for you. 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 ELM327, just the same as tapping a key
on the keyboard when using a terminal program. The
output pin (‘Busy’) is used by the ELM327 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 ELM327 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 ELM327. No need to worry
about the ELM327 becoming busy again after you
raise the RTS line at this point – once Busy goes low,
the ELM327 will wait (indefinitely) for your command. If
you do not use the RTS input on the ELM327, it must
be connected to a high logic level, as shown. Note that
Microprocessor Interfaces
1
2
3
4
5
6
7
8
9
+5V
X1
4.00MHz
C4
27pF
R27-30
470
+5V
C3
27pF
+5V
+5V
to
R15
to
R21
n.c.
+5V
327
L1-L4
your microprocessor
Rx
Rx
The ELM327 and your
microprocessor should
use the same 5V supply
Busy
RTS
76 of 94
ELM327
ELM327DSJ Elm Electronics – Circuits for the Hobbyist
www.elmelectronics.com
76


Need help? Post your question in this forum.

Forumrules


Report abuse

Libble takes abuse of its services very seriously. We're committed to dealing with such abuse according to the laws in your country of residence. When you submit a report, we'll investigate it and take the appropriate action. We'll get back to you only if we require additional details or have more information to share.

Product:

For example, Anti-Semitic content, racist content, or material that could result in a violent physical act.

For example, a credit card number, a personal identification number, or an unlisted home address. Note that email addresses and full names are not considered private information.

Forumrules

To achieve meaningful questions, we apply the following rules:

Register

Register getting emails for Elm 327 at:


You will receive an email to register for one or both of the options.


Get your user manual by e-mail

Enter your email address to receive the manual of Elm 327 in the language / languages: English as an attachment in your email.

The manual is 0,23 mb in size.

 

You will receive the manual in your email within minutes. If you have not received an email, then probably have entered the wrong email address or your mailbox is too full. In addition, it may be that your ISP may have a maximum size for emails to receive.

The manual is sent by email. Check your email

If you have not received an email with the manual within fifteen minutes, it may be that you have a entered a wrong email address or that your ISP has set a maximum size to receive email that is smaller than the size of the manual.

The email address you have provided is not correct.

Please check the email address and correct it.

Your question is posted on this page

Would you like to receive an email when new answers and questions are posted? Please enter your email address.



Info