Decoder Construction: MOV-8, ALU & SETAB
The card in question is the decoder which will take the value on the instruction bus and use it to decide which instruction class it represents. This class will then be used by the upcoming control card along with the sequencer pulses to operate the various control lines of the computer in the appropriate order. To begin with the decoder will recognise MOV8, ALU and SETAB instruction classes but there'll be more added later on.
Diving straight in to the construction I start with soldering down the status LEDs:
Next up are the card connectors:
With the soldering done it's on with the wire wrapping. There isn't much to do on this card - just the LED links, 'decision tree' lines between the relays and then the inbound opcode bits and outbound instruction class lines:
That's it for this card ... at least for now. It has just enough functionality to enable the computer to perform copying values between registers, loading values from the opcode and performing ALU operations. Before any of that will be possible I'll need to start constructing the sequencer ... again though, just enough to operate these three 8-cycle instructions. The sequencer will also be a break from the relatively straightforward pair of cards constructed recently ... so much so that the sequencer is spread over two cards as there's a lot to fit in.