More wiring

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Data, address and power buses ready

Finished the data and address buses and the power distribution. It’s only the clock circuit and the glue logic circuit wiring missing.

Final layout

Got a couple of sockets from Spiratronics (next day delivery!). So this is the final layout, all the sockets are placed.

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I still need to add resistors, capacitors and the crystal.

Wiring

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The data bus (green) and the address bus (yellow) wired. The data bus allows bytes transfered between the processor, the ROM and the RAM. The data byte consists of 8 bits, 8 wires carrying a bit each. The address bus allows the processor to chose data storage slots in the memory (RAM and ROM) for bytes to store or load. The address byte is 16 bits wide.
Wire wrapping is an old craft from the 1960-70’s. The idea is that a piece of wire is wrapped tight around square shaped pots protruding from the board. The blue tool shown in the previous post exerts tons of force per square inch that creates molecular bond between two pieces of unoxidised metal. Thus the wire wrapped connection is very reliable and gas tight. According to old electronic engineers wire wrapping can be 100% reliable if done properly. Also, since the wire is wrapped 7-8 times around the post, it offers greater surface are for contact, as opposed to soldering. Computers, including the Apollo Guidance Computer used for lunar landing and many space probes from the 60’s and 70’s were made with wire wrapping. This is the backplane of a PDP-8 computer from the 70’s.

PDP-8 backplane

A 6502 microcomputer

I started a new project. I’m building a clone of a 1979 British microcomputer.
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New life

Today I managed to hook power up the microprocessor and get some life signs. In the video I flip a switch to switch RUN mode on and off (a yellow LED shows the RUN state). Every time RUN mode is on, the microprocessor starts running and sending timing pulses on two pins to the memory. Now I only need to add some resistors, switches and the LED displays.

An 8-bit microcomputer – Cosmac Elf

Taking a break from my synth interface project and started building a microcomputer on breadboard. Why would anyone do that? To simply put, I realised I have no clue how a computer works. Considering that I want to make a living as a programmer and designer, that’s pretty¬†embarrassing. This computer called Cosmac Elf is simple enough to build and program. Since there’s no operating system, programs have to be entered in assembly language. In other words, I have to enter the program flipping switches that represent zeros and ones.

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New PCB, new challenges

I bought a cheap laminator and it didn’t work as well as I expected. Well, what did I expect from a ¬£14 laminator?

Instead I went back to the ye olde ironing which is exhausting but I’m getting better. Some nail remover and a cotton pad removes the paint perfectly, in case I screw up the board during the ironing phase.

Once I happily held my latest PCB, I realised the artwork is less then perfect. Tomorrow will make an other one.

Wednesday I’ll pick up a used laser printer (from Gumtree). Now I have to go to the corner shop to do the photocopying. Not anymore!