Showing posts from 2015

Sequencer Construction: 8-cycle FSM

I'm just about at the half way mark now for getting the computer to operate the MOV8, ALU and SETAB instructions. The easier cards are out of the way now ... time for the slightly more complex ones. In this post it's the sequencer cards which will deal with the 'when' of instructions by sending out timing pulses which the upcoming control cards will then use to operate the various control lines of the computer at the right time.

Note there that I did say sequencer 'cards' and not 'card' because there's two of them this time. This is the first part of the computer that will be constructed across two cards stacked together rather than all on a single card (the upcoming control unit will also be spread across two cards). This is for two reasons: firstly the sequencer needs access to more connections than a 'regular' card but secondly there'll be so much to fit in that it physically wouldn't fit on one card.

Working across two cards doe…

Decoder Construction: MOV-8, ALU & SETAB

In a change from prior form I'm combining the construction and testing of the next card in to a single post this time. Partly because this card is a nice easy one but also because it's the first card that I'll be partially constructing to begin with and then I'll return to it later to add further functionality.

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:
I've continued to use the same method of joining all the LED cathodes together with bits of trimmed off diode/LED legs as it takes the solder re…

Register Construction: Completed Instruction Register Full Test

Following on from my last post, and after popping in some relays, the instruction register is complete and looks like this:
As usual I've put a video together that demonstrates this card in operation. In this video I give a quick overview of the card and then demonstrate loading values in to the register and instruction bus. I also  demonstrate gating part of the instruction bus on to the data bus for the I2B (Immediate to Bus) functionality.

That's about all there is to say for this card as it's relatively simple and shares much of its design with the other register cards of the computer. The next card is also a simple one ... the decoder. This will take the value on the instruction bus and decide which instruction class it represents. This card will also be the first where I'll only partially construct it — just enough so that it can handle the SETAB, MOV8 and ALU instruction classes.

Register Construction: Instruction Register

There's been lots of theory going on in my recent posts but the time for design is over (for now) ... it's time to get constructing. The first card up in this batch is the instruction register and as it shares much of its design with the other register cards the construction is very similar.

The first step is to solder down the LEDs. Here's some pictures, front and back, of the card following this first round of soldering:
I've continued the trend of removing the negative wrapping post behind each LED again to make wiring up easier later on. I've also continued my 'other trend' of hunting for a good way of soldering up the cathodes on the LEDs ... this time I've folded each cathode leg over a piece of trimmed off LED anode leg to create a bridge between several cathodes and then soldered everything down. This seems to be the best way so far and the solder takes to the LED leg better than the using a piece of wire to bridge the cathodes. Unless I come u…