Solution:

The PCM-3724 is a bit different from PCL-731. Actually, it's 8255 compatible, and with additional 2 bytes : DIRECTION and GATE CONTROL. Following information just for your reference. Six 74HC245 chips (one for each port) buffer the PCM-3724's I/O lines to increase driving capacity. Because the 74HC245 is a bi-directional, tri-state line buffer, you need to set two additional I/O ports (BASE+8 and BASE+9) to control the direction of data flow. Moreover, please also take a look at following information. I'd test PCM-3724 with program DEBUG.EXE. Be sure to use a 50-pin flat cable to connect J3 (PORT1) and J4 (PORT2) of PCM-3724 before test. C:\WINDOWS>Debug -o 309, 0 <= Disable all Gates -o 303, 80 <= Set Port A0, Port B0 and Port C0 as OUTPUT -o 307, 9b <= Set Port A1, Port B1 and Port C1 as INPUT -o 308, 7 <= Set Port A0, Port B0 and Port C0 as OUTPUT, and set Port A1, Port B1 and Port C1 as INPUT -o 309, ff <= Enable all Gates - -o 300, aa <= Output AA to Port A0 -i 304 <= Read Port A1 AA - -o 301, 55 <= Output 55 to Port B0 -i 305 <= Read Port B1 55 - -o 302, 49 <= Output 49 to Port C0 -i 306 <= Read Port C1 49 -