BR16F84-1.07 ETC, BR16F84-1.07 Datasheet - Page 2

• Manufacturer Part Number: BR16F84-1.07
• Description: OBD II Interface Chip
• Manufacturer: ETC

ELECTRICAL and PHYSICAL CHARACTERISTICS:
This device is a CMOS microcontroller produced by Microchip Technologies. You can obtain detailed
specifications for the chip from Microchip data books, or on the Microchip website, so this section will only
provide a brief summary. It is available in several package designs and temperature ratings. The baseline
BR16F84-1.07 chip is a microchip 16F84A-20/P part, which is a commercial temperature range plastic 18 pin
DIP rated at 20 MHz. The device can be special ordered if other package designs, temp ratings, etc are
desirable.
TYPICAL APPLICATION CIRCUIT:
The typical application is a simple automotive scan tool using a PC or laptop as the host machine. The
interface to the PC is a serial link running at 19200 baud. Only 3 wires are needed, as no handshaking
signals are used. The serial output from the interface circuit is a 5 volt signal, which works well with most
PC's and laptops. The serial input is clipped and current limited, so it is capable of accepting almost any
signal voltage. The interface to the vehicle OBD bus is accomplished with a few external components and an
LM339 comparator chip. The connection to the vehicle uses 6 wires, assuming all three OBD protocols are to
be implemented. Operating voltage for the chip and associated circuits is small, and is derived from the
vehicle's 12V system on pin 16 of the OBD connector.
Refer to the schematic of a typical application. This design uses readily available components.
APPLICATION HINTS
(1) The cable to vehicle can be simple unshielded wires. This cable should be kept as short as possible, and
definitely no longer than 4 feet, especially for PWM operation. Somewhat longer cables could be used if the
circuit's termination resistors are replaced with lower values.
(2) The cable to Computer serial port can also be unshielded. The application circuit has been tested with
unshielded cables up to 30 Ft., but specific implementations may vary, so you may want to experiment if you
are attempting long runs. For every long runs, you might also wish to use an RS 232 transceiver chip in your
design.
(3) Circuit layout is not critical. The circuit has been tested on both hard wired perfboard prototypes and
plugboard breadboards. However, if your layout is very sloppy, you may want to add additional bypass
capacitors.
(4) Free software to utilize the application circuit is available for download. The program will run under DOS,
so it can be used on older computers as well as newer machines running windows. It is small enough that it
will fit on a DOS boot floppy, so you can still run it if your main operating system is not DOS compatible. The
computer need not even have a hard drive.
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