ADVANCED VEHICLE TECHNOLOGIES, Inc.
AVT-715 Dual J1850 INTERFACE
(VPW and PWM)
RS-232/422 Unit Technical Summary
INTRODUCTION
The AVT-715 comes as a ready-to-use package consisting of a hardware interface
unit (the HIU consists of the AVT-715 Interface board housed in an enclosure);
the Controller software; a serial cable assembly; and an OBD-II compatible
cable assembly. Connecting the AVT-715 HIU to a subject vehicle is quick
and easy and no tools are required.
The AVT-715OEM module consists of the AVT-715 interface board only.
The Society of Automotive Engineers (SAE) has adopted a specification
known as J1850 Class B Data Communications Network Interface. This specification
describes two forms of a multiplex bus structure intended for use in a
vehicle. The two forms of this multiplex bus are known as Pulse Width Modulation
(PWM) and Variable Pulse Width (VPW). The AVT-715 Hardware Interface Unit
implements both versions of the J1850 standard. (Simultaneous operations
are not permitted.)
Additionally, the HIU conforms to the Ford Motor Company Standard Corporate
Protocol (SCP) which defines network traffic management, message construction,
and other protocol issues. The AVT-715 is fully compatible with any similarly
equipped Ford Motor Company or Mazda product.
The AVT-715 Dual J1850 Interface unit provides the following functions:
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Isolated electrical interface between the subject vehicle and the control
computer.
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Protocol/data conversion between the vehicle J1850 multiplex bus and the
serial data link to the control computer.
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Passive network traffic monitor.
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Performs all functions of an active SCP qualified network node.
Hardware Connections
Connecting the AVT-715 HIU to the subject vehicle is accomplished via the
OBD-II compatible cable assembly supplied with the HIU. (Note: this cable
is not supplied with the OEM module.) The cable assembly has a DA-15S connector
on one end and an OBD-II compatible connector on the other end. The AVT-715
HIU receives operating power, J1850 bus signals, and grounds from the subject
vehicle through this cable assembly.
The AVT-715 HIU is connected to the control computer via the supplied
9 pin cable assembly. (Note: this cable is not supplied with the AVT-715
OEM module.) The supplied cable assembly is compatible with a PC-AT standard
9 pin RS-232 connection.
No other connections or installation is required.
Specifications and Requirements
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PC-AT compatible computer.
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486 or higher processor.
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Minimum of 8 MBytes of memory.
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Minimum of 1.5 MBytes of hard disk drive space.
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VGA Monitor.
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Mouse (recommended).
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MS-DOS 5.0 or later.
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MS-Windows 3.1x.
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Serial port, either RS-232 or RS-422.
AVT-715 Hardware Interface Unit:
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Overall size: 6.7 wide x 4.75 deep x 2.25 high (inches).
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Weight: 16 oz.
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+12 volts (nominal) from subject vehicle.
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Power dissipation: 1.8 watts (nominal).
Hardware Configuration
The AVT-715 HIU serial communications link to the control computer can
be configured for either RS-232 or RS-422 operation . The data rate for
the
serial link can be configured for 9.6k, 19.2k, 38.4k, or 57.6k baud rate.
These configuration selections are set by jumpers and connectors on the
AVT-715 Interface Board. (Note: documentation by other manufacturers may
make reference to 56k baud. This is usually the same as what we refer to
as 57.6k baud; the actual baud rate.)
AVT-715 Controller Software
The AVT-715 Controller software is an MS-Windows 3.1x compatible program
that provides the user with direct control and observation of the operation
of the AVT-715 HIU as well as a data logging function, file download capability,
and network monitor function.
Menus and Windows
The main menu bar selections are FILE, STATES, ADMINISTRATION, TOOLS, and
HELP.
Selecting STATES | COMMAND opens the AVT-715 Command Dialog and Console
window. In this window the operator can:
-
Manually enter commands to the AVT-715 hex digits.
-
Observe all responses from the AVT-715 unit.
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Select a file for automatic downloading to the AVT-715 unit.
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Select the logging function in which all activity is logged to disk.
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Select the date and time tag function in which all activity is date and
time tagged.
Selecting STATES | NETWORK MONITOR opens the AVT-715 Network Monitor window.
From this window the operator can:
-
Observe all responses from the AVT-715 unit.
-
Select the logging function in which all activity is logged to disk.
-
Select the date and time tag function in which all activity is date and
time tagged.
The ADMINISTRATION | CONFIGURATION PARAMETERS window offers the operator
the following selections:
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Network mode (VPW or PWM).
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Default download file directory specification.
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Default log file directory specification.
The ADMINISTRATION | COMMUNICATIONS PARAMETERS window offers the operator
the following selection:
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Com port selection (COM1, COM2, COM3, or COM4).
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Baud rate selection (9600, 19200, 38400, 57600).
The TOOLS | MESSAGES menu selection opens a window for the display of AVT-715
Controller status and error messages.
Hardware Interface Unit
The AVT-715 Hardware Interface Unit (HIU) consists of the AVT-715 Interface
Board housed in a rugged polycarbonate enclosure with internal cable assemblies,
switch, and external cable assemblies. The two connections to the HIU are
to the subject vehicle and the control computer.
The HIU provides an isolated electrical interface between the control
computer and the vehicle. The AVT-715 HIU is connected directly to the
vehicle and derives its operating power from the vehicle. The serial interface
to the control computer is electrically isolated from the vehicle electrical
and electronic systems. This is done to prevent damage to the control computer
due to spikes or surges from the vehicle electrical system. It is not recommended
that the control computer be connected directly to the vehicle electrical
system.
The AVT-715 hardware interface unit performs the data and protocol conversion
functions. For the VPW mode of operation the HIU utilizes the Harris HIP7030A0
J1850 VPW microcontroller device along with the Harris HIP 7020 bus transceiver.
For the PWM mode of operation the HIU utilizes the Motorola/Ford HBCC device
and a Ford bus transceiver design.
The serial communications interface function of the HIU is provided
by a Philips Serial Communications Controller (SCC) device. The RS-232
and RS-422 line drivers and receivers are contained in an electrically
isolated section of the AVT-715 Interface board. Signals are coupled through
optical isolators and power is supplied by an isolated DC-DC converter.
AVT-715 Operation
All communications between the HIU and the subject vehicle are in conformance
with SAE Standard J1850 and all related standards and recommended practices.
When in the PWM mode of operation, the HIU is compliant with the Ford SCP.
All communications between the AVT-715 HIU and the control computer conform,
at the physical interface, to either EIA-RS-232 or RS-422 standards (as
selected by the user).
The structure and protocol of communications between the control computer
and the HIU are such that all data is transferred in packets. The size
of each data packet varies from 1 byte to 16 bytes (inclusive). The first
byte in each data packet is the header byte and is used to convey information
only between the control computer and the microcontroller in the HIU. All
bytes within a packet are binary data.
The header byte is divided into the upper nibble and lower nibble. The
upper nibble indicates what information the data packet is conveying. The
lower nibble is the count of the number of bytes that follow the header
byte. The meaning of the upper nibble of the header byte depends on which
direction the data packet is moving; whether to or from the control computer.
Messages from the control computer to the AVT-715 HIU are known as Commands.
Message from the HIU to the control computer are known as Responses. The
following are excerpts from the Users Manual. Please consult the latest
revision manual for up-to-date information.
Figure 1 AVT-715 Hardware Interface Unit Block Diagram
Command Header Byte
This byte is prepended onto a packet transmitted by the control computer
to the HIU.
Low nibble, bits b3 - b0: Byte count (how many bytes to follow); may
be zero when the message is only a status or error message.
High nibble, bits b7 - b4 (undefined or reserved values are not listed):
$0x: This is a valid packet for transmission (the null byte 00 is
ignored).
$2x: Reset command, must be followed by a byte specifying the device
to be reset.
{$21 $01: Reset the HBCC device.}
{$21 $02: Reset the SCC device.}
{$21 $03: Reserved.}
{$21 $04: Reset FIFO #1.}
{$21 $05: Reset FIFO #2.}
$7x: HIP7030A0 write RAM (address byte, data byte, follow).
$8x: HIP7030A0 read RAM (address byte, requested bytes [<=$0E],
follow).
$9x: Hardware Register #1 write (data byte follows).
$Ax: Hardware Register #1 read.
$Bx: Request firmware version number.
$Cx: 4x mode command. ($C0: request status; $C1 $00: Off; $C1 $01:
On).
$Dx: Request operational mode.
$Ex: Switch to PWM mode, must be followed by $CC. [$E1 $CC]
$Fx: Hardware unit Re-Start command, must be followed by $A5. [$F1
$A5]
Response Header Byte
This byte is prepended onto a packet transmitted by the HIU to the control
computer.
Low nibble, bits b3 - b0: Byte count (how many bytes to follow); may
be zero when the message is only a status or error message.
High nibble, bits b7 - b4 (undefined or reserved values are not listed):
$0x: This is a valid packet received from the bus.
$2x: Error message, error byte(s) follow (error messages defined separately).
$3x: Command message error, error header byte follows.
$7x: HIP7030A0 read RAM error, requested byte count greater than $0E.
$8x: HBCC read RAM (address byte, data bytes, follow).
$9x: Board status information byte follows:
{$9x $00: Reserved.}
{$9x $01: Reserved.}
{$9x $02: SCC initializations complete.}
{$9x $03: HBCC initializations complete.}
{$9x $04: Firmware version number follows.}
{$9x $05: VPW operation (Harris).}
{$9x $06: PWM operation (Motorola).}
$Ax: Message status information. ($A1 $10 arbitration lost, message
flushed.)
$Bx: Transmit message too long (> 11).
$Cx: 4x mode status response. ($C1 $00: Off; $C1 $01: On).
$Dx: Hardware Register #1 read, data byte follows.
$Ex: Errors: $E0: buffer open failure; $E1: SENDEC error, SEDSR follows.
Received Message Status Byte Definitions
The received message status byte always follows the header byte, even
if the status byte is the result of transmitting a message.
Bit Definition
0: CRC error.
1: Incomplete message (incorrect number of bits).
2: Break received.
3: IFR data.
4: Lost arbitration.
5: Transmission successful.
6: From this device.
7: Bad message.
Examples
Example #1: Want to request the current operational mode.
Command: D0.
Explanation: The HIU will respond with: 91 05. The 9 indicates a board
response, the 1 indicates one byte follows, and the 05 indicates VPW
mode.
Example #2: Want to send a message out on the bus.
Command: 04 32 89 AC 5F.
The HIU will respond with: 01 60. The 0 indicates a received message
and the 1 indicates only one byte, which is the received message status
byte. The 60 indicates that bits 6 and 5 are set which means the received
message was from this device and the transmission was successful. (Messages
transmitted by the AVT-715 are received by the AVT-715, are checked, but
are not echoed back to the controller. Only a status byte is passed to
the controller to indicate the status of the transmitted message.)
Company Overview
Advanced Vehicle Technologies, Inc. is dedicated to providing affordable
hardware, software, and technical support to the developers and users of
vehicle based multiplex networks. We offer other vehicle multiplex bus
products including the AVT-1850 A J1850 VPW Development System and the
AVT-921 Dual J1850 Interface (an 8-bit ISA bus printed circuit board for
installation in a host computer). Contact the factory for information on
these products and our latest offerings.
The engineering staff at AVT, Inc. has combined experience on a number
of multiplex bus standards including: J1850 VPW and PWM and ISO-9141 and
9141-2. Members of the staff are available to provide assistance on the
use of any of AVTs products.
AVT engineering staff members are available to provide dedicated engineering
support for a customer project. Through a simple contractual arrangement,
a customer is able to tap into AVTs knowledge and experience base.
Information on any of the products or engineering support that Advanced
Vehicle Technologies can provide is available by calling, faxing, or writing.
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