AVT-921 - A Dual J1850 Interface (VPW and PWM)
J1850 Vehicle Networks
SAE standard J1850 is gaining widespread acceptance by the automobile
manufacturers. With the advent of this new network architecture, engineers,
technicians, and others need to be able to test, monitor, and communicate
with a J1850 network equipped vehicle.
Complicating this issue is the fact that a J1850 network may be implemented in either of two incompatible versions: Variable Pulse Width (VPW) or Pulse Width Modulation (PWM).
The AVT Solution
The AVT-921 Dual J1850 Interface is a printed circuit board that, when
installed in a personal computer, permits the user to connect the PC directly
to a J1850 equipped vehicle. The user can then monitor network traffic,
log network activity, analyze communications, simulate a network node,
and perform a number of other network functions. Operation of the AVT-921
Dual J1850 Interface is controlled via software commands from the host
to the hardware.
By combining the interface functions for both VPW and PWM modes into a single unit the investment by the user is reduced and flexibility is enhanced.
Available for the AVT-921 are controller software and a vehicle compatible cable assembly.
The AVT-921 Controller Software
The AVT-921 Controller software can operate in a command mode which
permits operator introduction of network messages onto the J1850 bus. This
mode permits the testing of node interactions to specific message sequences
and other user defined test scenarios. Commands can be entered individually
or downloaded via a batch file.
A network monitor mode permits the capture and display of bus traffic. Options to timetag and log the data to a file ensures an historical record of network activity for later analysis. The disk logging function is limited only by the amount of available disk space.
The Controller software for the AVT-921 was designed to support engineering uses (testing, data acquisition, etc.). Advanced Vehicle Technologies, Inc. plans on developing software to support diagnostic functions. Contact the factory for updated information.
The AVT-921 Controller runs on PC-AT machines under Windows 3.1x. A 66 MHz 80486 with 8 MB of memory and at least 2 MB of disk space is the minimum recommended host.
The AVT-921 Hardware
The AVT-921 is an ISA bus board designed for installation in an 8-bit
ISA slot of a PC-AT or compatible computer. It provides an isolated electrical
interface between the host computer and the J1850 network of a subject
vehicle. The AVT-921 board performs the necessary protocol conversions
and all required communications translations allowing the user to communicate
with the vehicle network.
SAE standard J1850 specifies a Variable Pulse Width (VPW) version with a bit rate of 10.4 Kbits/sec. The standard also specifies a Pulse Width Modulation (PWM) version with a bit rate of 41.6 Kbits/sec. The AVT-921 was designed to communicate using both of these versions of the J1850 standard. (Simultaneous operations are not permitted.)
The AVT-921 is capable of conducting both transmit and receive operations, while in the VPW mode, at 4 times the normal speed. (Operations at 4X speed in VPW may be required for some GM Class 2 modes.) Additionally, the architecture of the AVT-921 ensures that it is compliant with the Ford Motor Company Standard Corporate Protocol (SCP).
The AVT-921 printed circuit card is in the XT form factor and 3/4 length. The board contains a microcontroller, RAM, ROM, both VPW and PWM bus interfaces, and an ISA bus interface. The AVT-921 is mapped into empty memory space of the host computer. On-board DIP switches permit the user to select the base address of the AVT-921 board. The board occupies only 16 bytes of memory space in the host.
A User’s Manual is included with the AVT-921 (it includes technical information on communications between the board and the host). Also available is a cable assembly that allows direct connection of the AVT-921 to the subject vehicle through the OBD-II connector now found in nearly all vehicles sold in the U.S.
All AVT equipment is warranted for one year from date of purchase. Additionally, all customers get free software and firmware upgrades for one year from date of purchase. Telephone technical support is available.
Specifications
Size: 4.2 x 10.0 inches.
Weight: 7 ounces (board only).
Voltage: +5 VDC and +12 VDC (from the host computer), +12 VDC (from
vehicle).
Power: 1.5 watts (nominal).
Host interface: 8-bit ISA bus, memory mapped, base address selectable.
Connectors: 8-bit ISA bus, DA-15P (to vehicle OBD-II).
Microcontroller: HIP 7030A0 (Harris), 68HC05 core.