2650 single step

22 2650 single step It can be very handy if the micro- processor can be put into single step mode when debugging home made programs. This little extra can be realized by constructing the circuit described in this article. Readers who own a 2650 μP — amongst them a lot of game computer owners — have had to do without this facility .. . until now. The 2650 can be put into single step mode by making the 1 P believe that it is connected to a very slow memory. Consequently, the address and data bus remain valid during each read or write mode until a switch is pressed. In this way, all addresses and data can be checked step-by-step without running into problems. The circuit, consisting of two flip- flops, a switch and a logic gate, uses the OPREQ (operation request) and OPACK (operation acknowledge) signals to combine them into a "new" PACK signal. The "old" OPACK signal is combined to output Q of FF2 via OR gate Nl. The original OPACK line must be broken and particular attention p...