ELM325
J1708 Interpreter
Description
Features
With the advent of electronic engine controls,
• Supports both SAE J1587 and J1922
• High speed RS232 interface
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.
• Works with standard RS485 transceivers
• Fully configurable with AT commands
• Wide operating voltage range (1.8 to 5.5V)
• Low power CMOS design
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.
Connection Diagram
PDIP and SOIC
(top view)
1
2
3
4
5
6
7
14
13
12
11
10
9
VDD
XT1
VSS
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.
RO
XT2
RE
InvDE
DE
RS232 Rx
RS232 Tx
RS Rx LED
J Tx LED
J Rx LED
RS Tx LED
Applications
8
• Diagnostic trouble code readers
• Heavy duty vehicle scan tools
• Teaching aids
• ECU Simulators
3.58 MHz
Block Diagram
InvDE
2
3
XT1
XT2
4
Timing and
Control
13
11
RO
5
6
RS232 Rx
RS232 Tx
DE
RS232
Interface
J1708
Interface
J1587/1922
Interpreter
12
RE
7
8
10
9
RS Rx LED
RS Tx LED
J Tx LED
J Rx LED
ELM325DSA
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