software RAM tester

31 address decoder or buffer, timing faults or any of the various other problems that can (and do) occur. Of course a logic analyser would make the job of trouble shooting a lot easier, but for many people such equipment is in the category de- scribed as "Very nice, but...". So here is a program that uses the computer to trace faults in RAMs and display them on the oscillos- cope screen. What could be simpler? The program example (for a Z80) shows the principle of this type of software. The address of the memory location under scrutiny ("TEST") is loaded into HL. In the program loop (called "LOOP" for some strange reason) the contents of this memory location is read, and then inverted (so "1" becomes "0" and vice versa) and finally it is written into the same memory location. This oper- ation is repeated ad infinitum. The write pulse of the system is used to trigger an oscilloscope. Thus the scope is triggered once every time the "LOOP" is executed and thus the data is displayed o...