2-word ROM for Wang 600
2-word Test ROM for Wang 600
This is a powerful tool for detailed diagnosis of logic engine faults. It allows one or two words of microcode to be set up on switches and altered as needed.
One word appears at every even ROM address and the other word at every odd address. This allows ROM addressing to be tested by setting the ROM word address fields to anything desired and ensuring that this address is propagated from the ROM word to the address buffers. ROM jumps can likewise be tested by jumping between the two words.
The remaining microcode bits can be used to test very specific functions of the logic engine. Single instruction loops allow one function to be repeated while two-instruction loops allow toggling of a function. It is surprising how much complexity may be encoded into one or two microcode words.
Design and Use
The design is very simple, two banks of switches select the microcode data lines to be pulled low (NB see below), the bank being selected by the lowest order microcode address bit. The address bits are buffered to drive LED indicators and the selected microcode bank is also indicated by an LED.
The desired microcode is dialled into the rotary switches as its hex representation, noting that some switches combine two microcode fields (for economy of switches).
Note that for the 600 Test ROM the microcode must be entered into the switches as its complement. This is because the 600 microcode is encoded as active-low but the emulator was designed for ‘parts readily to hand’ where the rotary switches were active-high.
Obtaining a Test ROM
ROM Emulators are available from DoPECC in a number of forms:
- fully built
- bare PCB
- design files
- loan and return
Contact DoPECC to discuss your situation and best solution