Wiring harness test circuit is composed of 8 circuit
boards. There are 2 CPLD chips in each board, one CPLD
chip was used to send test signal, and the other used to
receive the test results. The CPLD interior logic circuit is
shown as in figure 4. The main units is composed of a 6-64
decoder and a 64-1 multiplexer,which are realized with
VHDL language and are used to select the wiring harness
test address and transmit the test data. There are also data
latches and logic control circuits on the CPLD. Because the
apparatus realizes up to 512 points test, each CPLD need to
perform 64 nodes test and data transmission. One or more
circuit board was selected by the chip select signal initiated