After giving you a general tour of the ALU of the Bentium Pro and the carry select circuitry I want to move onto describing the flags register and how the flags are evaluated. As a reminder, the Bentium Pro has four flags: Carry. This can contain the carry/borrow from the adder and also the bit …. Read More
I was thinking recently about OR gates. We normally do these with TTL logic chips but I wondered whether it would be possible to do the same thing with diodes. A quick Google showed that this was not merely a workable idea but something which has a name – ‘diode logic‘ – and which has …. Read More
The ALU on Ben Eater’s original Bentium 8-bit computer has two operations: add (ADD) and subtract (SUB). This gives his design the ability to add and subtract 8-bit numbers. But if you want to add or subtract larger numbers then you need more than 8 bits. You could do this by expanding to a 16-bit …. Read More
Last year I built Ben Eater’s 8-bit breadboard computer, which taught me a lot about how processors work. But with only 16 bytes of memory it’s not really usable for any kind of real world tasks. As soon as I’d finished it I knew I wanted to make some upgrades. And when I looked at …. Read More
If you’re working (or playing) with digital electronics then you’ll probably want to display your data data on hex displays at some point. Normally this involves using some kind of decoder to turn your data into something that can drive a 7-segment display. Which means extra chips, extra wires and extra breadboard space. I set …. Read More