Showing posts from April, 2014

Register Design: Dual Output 8-bit Register

In the last post I introduced the design for the A/D register card (which as its name suggests contains the A and D 8-bit registers). I'm now making a start on the design for the B/C register card and although its pretty much the same as the A/D card there's an extra complexity because the B/C registers additionally feed the ALU B and C inputs.

For the A and D registers I ended up with the following circuit per 8-bit register:
In this design the spare pad on the left of each of the lower relays feeds an LED to show the status of each register bit. This pad is isolated from the register bit circuitry itself by making use of the second DPDT switch on each bit relay. The B and C registers will also need this LED feed but additionally need to provide a permanent feed of the current value in each register bit to the ALU. However, I can't just piggyback on the pad used to light the LED because there's a risk that the LEDs could light up in error if anything back feeds up the…

Register Design: A and D 8-bit Registers

In the last post I introduced the design for a general purpose 8-bit register. This post covers taking two of those registers along with status LEDs and gating relays to implement the full A and D registers.

So, diving straight in, here is what the main bit relays look like for the two 8-bit registers when placed on the usual 55 x 40 hole pad board (excluding wire links):
Each of the relays above stores a single 1-bit value so there's 16-bits worth in total (which could all be used together if we were making a 16-bit register) or two lots of 8-bits (for our two 8-bit registers). Each of the 1-bit register relays need gating to and from the data bus so that the values stored don't conflict with any other value on the data bus. With these additional control and gating relays added we get the following (this time including internal wire links in the 1-bit register relays and result links between the 1-bit register relays and the gating relays):
So, that's it for relays on th…

Register Design: General Purpose 8-bit Register

This post covers the design of a general purpose 8-bit register that can be loaded from the data bus and then selected back to the data bus at a later time. This permits temporary storage of 8-bit values whilst performing various operations, for example, ALU functions. This post goes back over some of the ground already covered by the design of the condition registers which are a slightly simplified version of the registers detailed here.

In the most basic terms we can store a single bit in a relay as follows:
In its initial state the register is off and both the IN and HOLD inputs are off. A value is applied to the IN connection and then the HOLD input is set on and the value at IN removed. If the value was set then the relay would be activated allowing the HOLD input to keep the relay on. The relay will then remain on until the HOLD input is set off. Separately to this power is supplied directly to one of the other relay switches and provides an isolated source of the value held in …

Enclosure Update: Laser Cutting

I couldn't resist it any longer ... I've ordered the laser cut parts for the case doors, sides and bay floor/ceilings. I did say I'd wait for my chosen laser cut website to put out a free delivery offer but I ended up crumbling under the weight of my own impatience. Needless to say within 24 hours of placing my order they announced a free delivery offer for the end of April ... c'est la vie and all that jazz.

Oh, and I hope you like pictures because this post is a bit of an image-fest.

I covered the design of the floor and ceiling panels in my recent post but for the hard of searching here's the cut file for these panels (with cut lines beefed up so you can see them better — the original file has the lines set to 0.01mm):
As you can probably see, there's eight identical panels which form the four sets of ceilings and floors that fit in to each of the card bays. Here's a SketchUp rendering again of how one of those bays will end up looking:
I've chosen t…