Hello dear friends,
I have some experience with 8051 programming in Assembler.
Recently I have to repair several Vehicle ECU(Electronic Control Unit). The ECU employs two 80C535 microprocessor in the unit, so I wanted to test the 80C535.
Since it is difficult to find an 80C535 Tester, I decided to build a simple one myself. With many 8051 circuits are in the Internet, I was succeded in building an 80C31 Development Board. It can be connected to PC running Hyperterminal via RS232 port, and has a Monitor Program in the EPROM. I can download a hex format 80C31 program from the PC into the board's RAM and run it. It has also an 8 bit port to connect to the outside world.
Afterwards, I built a same board, but I substituted an 80C535 in place of the 80C31. I implemented some modification of course :
1. Set the Reset pin normally high, merely by connecting a 10
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