Showing posts from November, 2017

Memory Test

I've covered the construction of the upper and lower memory cards in my last two posts ... it's now time to bring those two cards together to form the memory unit proper and give it all a test.

Here's the upper card (in close up and at a rakish angle) ...

... and here's the lower memory card (at an equally rakish angle) ...

... and when sandwiched together here's how the memory unit as a whole looks:

As for all the cards constructed before it I can whip out my trusty breadboard to test the memory unit in isolation before hooking it up to the rest of the computer:

Here I've hooked the data bus up to the bar display but it can be switched over to the left hand DIP switches depending on whether I'm reading or setting a value from/to memory. The address bus comes over to the middle and right DIP switches. The eagle eyed of you out there might have noticed that leaves us four bits short of the full address bus but that's OK for testing purposes. Finally the…

Memory Construction (Part 2 of 2)

In my last post I made a start on the memory unit construction with the lower memory card. The lower card centres around the memory IC which runs at 5V. The upper memory card picks up the task of converting the data and address bus coming in from the rest of the computer (running at 12V) to the 5V needed by the memory IC.

The LEDs and backplane connectors were soldered down in my last post so we can jump straight to adding the card interconnects which pass the local address/data busses to the lower card:

These interconnects mate with the matching sockets on the lower card and when sandwiched together the two cards form the memory unit.

Next job is to solder down all the relay sockets and wire wrap posts. In my last post I mentioned that the upper memory card is quite densely populated as a large number of relays are required to handle all the data and address bus conversion. On previous cards I've soldered down two rows of turned pin sockets with the wire wrap posts alongside for…

Memory Construction (Part 1 of 2)

It's time to make a start on the construction of the memory unit and as mentioned in my last post this one is a bit more complex than 'boring old registers' and so I'll split it over two posts. Let's dive in with the easy part - soldering down the LEDs and backplane connectors:

For the lower memory card there are 16 LEDs for the 16-bit address bus and 8 LEDs for the 8-bit data bus. Both of these busses are 'local' to the memory unit and operate on +5V and ground as covered in my post on the memory unit design. Unfortunately I've messed up here a bit as I've merrily gone and soldered down the same LEDs I use on all the other cards ... the 12V ones. Although these LEDs will work with 5V they won't be as bright due to the internal resistor in each being rated for 12V operation. A bit of a silly mistake to make but it's done and I'm not so upset by it that it's worth changing them over ... I only realised when I tested the card and noti…

Program Counter Construction

In my last couple of posts I've been slightly distracted by some 'miscellany' but now I return to form and crack on with constructing the program counter. The program counter is effectively two 8bit registers bolted together and wired out slightly differently using the address bus rather than data bus. As usual I'll start with soldering down the LEDs:
This should all be very familiar now and there's nothing unusual about these LEDs compared to previous cards. I'm just about at the point now where I've 'perfected' the way of soldering and wiring these up after many iterations on previous cards. Next up is backplane connectors and relay sockets:
Again, all very similar to previous cards. To be frank though I'm starting to find fitting the individual relay sockets a bit tedious which means it's time to rethink how I approach this. On the upcoming memory card I'll be tackling these in a slightly different way which will make construction a …