Circuit Description

Program ROM checksum error detection is internal. No external circuits are involved. For DTC to set, microprocessor must run program to detect a check sum error after each "power up". The only requirements are voltage and ground. This program runs even if voltage is out of operating range.

Microprocessor retains an inverse copy of digital value stored in certain blocks of memory in calibration ROM. Microprocessor then reads information from certain blocks and adds stored inverse value to current value. If they do not equal 0, the microprocessor will set DTC B1013.

When DTC is set, microprocessor reverts to base operation values programed for those blocks of data that have failed check sum test. Blocks of data that have not failed check sum test are not affected. DTC will clear when microprocessor runs successful check sum test of calibration ROM.