ELM325
J1708 Interpreter
Description
With the advent of electronic engine controls,
many vehicles also adopted some form of diagnostic
tools to help monitor their operation. As more
modules began to be used in vehicles, there was
also a need for the devices to share information
rather than each independently obtain this from
separate sensors.
In the 1980’s, the SAE J1708 standard was
created to provide a specification for a common data
bus to be used in heavy duty vehicles. It used
RS485 wiring (already proven to be reliable in noisy
environments), and a UART-based low speed data
format. The SAE J1587 standard followed a few
years later to describe the mechanism by which
messages and data should be sent between vehicle
modules.
The ELM325 allows a PC or similar device to be
used to monitor and query devices on a J1708 data
bus, using simple commands that can be sent from
almost any terminal program. It is able to work with
either the J1587 or the J1922 data formats.
Features
• Supports both SAE J1587 and J1922
• High speed RS232 interface
• Works with standard RS485 transceivers
• Fully configurable with AT commands
• Wide operating voltage range (1.8 to 5.5V)
• Low power CMOS design
Connection Diagram
PDIP and SOIC
(top view)
V
DD
XT1
XT2
InvDE
RS232 Rx
1
2
3
4
5
6
7
14
13
12
11
10
9
8
V
SS
RO
RE
DE
J Tx LED
J Rx LED
RS Tx LED
Applications
• Diagnostic trouble code readers
• Heavy duty vehicle scan tools
• Teaching aids
• ECU Simulators
RS232 Tx
RS Rx LED
Block Diagram
XT1
2
3.58 MHz
InvDE
3
XT2
4
Timing and
Control
RS232 Rx
RS232 Tx
5
13
RO
DE
6
RS232
Interface
J1587/1922
Interpreter
J1708
Interface
11
12
RE
RS Rx LED
RS Tx LED
7
8
10
9
J Tx LED
J Rx LED
ELM325DSA
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