AVT-931 - A Dual J1850 Interface (VPW and PWM) in PC/104 form factor
J1850 Vehicle Networks
SAE standard J1850 is gaining widespread acceptance by automobile manufacturers.
With the appearance of this 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-931 Dual J1850 Interface is a PC/104 form factor board designed
to be mated to a PC/104 host computer. The AVT-931 can be connected directly
to a J1850 equipped vehicle. The user then is able to monitor network traffic,
log network activity, analyze communications, simulate a network node,
transmit messages, and perform a variety of other network functions. Operation
of the AVT-931 is controlled by software commands from the host to the
hardware interface.
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.
The AVT-931 Hardware
The AVT-931 Interface board conforms to the PC/104 form factor. It
is an 8-bit board but is equipped with 16-bit stackthrough connectors.
(Alternate arrangements may be available upon request.)
It provides an electrically isolated interface between the host computer and the J1850 network of the vehicle under test. The AVT-931 board performs the necessary protocol conversions and all required communications translations allowing the user’s host computer 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-931
was designed to communicate using both of these versions of the J1850 standard.
(Simultaneous operations are not permitted.)
The AVT-931 is capable of conducting both transmit and receive operations (in 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-931 ensures that it is compliant with the Ford Motor Company Standard Corporate Protocol (SCP).
The AVT-931 board utilizes a microcontroller with on-chip RAM and ROM. Also on the board are the VPW and PWM bus interface devices and an ISA bus interface (to the host). The AVT-931 is mapped into empty memory space of the host computer. On-board DIP switches permit the user to select the base address of the Interface board. The board occupies only 16 bytes of memory space in the host. The host interface consists of one read-write hardware register (with control and status bits), one read only register (FIFO), and one write only register (FIFO). The two FIFOs are implemented as a set of two way mailboxes. All communications between the host and interface board consist of commands and responses passed via the FIFOs.
A hardware User’s Manual is included with the AVT-931. It contains technical information on communications between the board and the host, connectors, memory map, and all other information that a user would need. Available separately is a cable set that allows the AVT-931 to be connected directly to the vehicle under test 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: 3.8 x 4.3 x 0.5 inches.
Weight: 3.5 ounces.
Voltage: +5 VDC and +12 VDC (from host computer), +12 VDC (from vehicle,
optional).
Power: 1.2 watts (nominal).
Host interface: 8-bit ISA bus, memory mapped, base address selectable.
Connectors: 16-bit stackthrough and 16 pin header to the vehicle OBD-II
connector.
Microcontroller: HC11KA2 (Motorola).
Controller Software
• Available for the AVT-931 is Controller software originally designed
for the AVT-921 Dual J1850 Interface.
• 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 Controller software was designed to support engineering uses
(testing, data acquisition, etc.) and includes a number of functions that
are useful in an engineering and test environment.
• The AVT-921 Controller software runs on a 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.