three-state indicator - handy unit for 6502 users

handy unit for 6502 users The circuit presented here was designed primarily for 6502 users. It indicates which of the following signals occurred last RESET = RES = 0 INTERRUPT REQUEST = IRQ = 0 NON-MASKABLE INTERRUPT = NMI = 0 This information is particularly helpful in the event of failure of a 6502 microprocessor system. It is equally useful during the handling of specific software for such a system. The circuit effectively forms a three- state indicator and consists of three NAND gate latches. Each latch is set by one of the three signals men- tioned above. When that happens, the latch in question resets the other two latches via the relevant diodes. At the same time the high Q level causes the relevant transistor to con- duct and this in turn makes the ap- propriate LED light. This LED will re- main on until one of the other two latches is set. Arg0— any J.C. (6502) 1M 0 system 0— N1 ... N6 = 1%x 4011; x 4093 T1 ... T3 = BC 547B D4 ... D12 = 1N4148 7-92 three-state indicat...