Z80 System B update

So, the only thing lacking hardwarewise on the Z80 system I'm building, is the I/O. Once more, I was very inspired by Donn Stewarts z80 project in my port control logic, though I've made a connector for an external "terminal".

As you see, the "terminal" is really just two ports of LEDS as output and slide switches as input. The cable goes to a 40 pin DIL ribbon connector and socket, to port select and latching, etc.

This is the interface board, using the 74LS139 as address decoder/port selector, and 74LS244 for input buffers, 74LS373 for display latches. Still needs wiring.

And Wouldn't you know: The board cracked! when i was scoring the rectangular cutouts for the switches! The pcb material were.. not good; had a consistency as wet crackers, and flaked like slate, meaning when it cracked (the entire bottom right quarter) it sliced  the palm of my hand right up! but i was able to fix it (the board, that is; the hand takes care of itself) by means of screwing on a little piece of pcb on the underside, and solder some of the traces back. Holds quite well. 

Memory circuit wired

This is the memory card for my Z80 system. It contains a single 8x2k SRAM, the 6116-2, one of my favorite SRAM's, because its name is a palindrome. A 2716 EPROM of same size (and pin compatible, by the way) is used as system ROM. Address decoding for chip select with a 74139. Memory decoding entirely after Donn Stewart's Z80 computer. A more refined point-to-point wiring technique than with the indicator card, and i think it's really neat! Maybe even more so than wire-wrap. 

Using the same wire to make little ties for the wire bundles. 

For this method, start by wiring power, then control logic, and THEN DATA and ADDRESS buses, as you see, they are the ones who takes up space. Make sure that the wires are approximately the right length to be routed, and then after soldering of a bundle, begin "neating" with wire ties, either free floating or though holes in the PCB. excess length can be huddled up at one end (here, at the connector).