Clock

Clocking in...

The completed module minus it's 74HCT04.

Makes sense to start with the smallest module of the five, the CPU Clock/Reset. The clock itself consists of 6 passive components and an 74HCT04 and is the same design used in Grant Searle's Simple Z80 Computer and various other Z80 projects. Although the module takes up a full slot on the backplane, it occupies only 4 lines on the RC2014's bus and connects to the bus by means of an 8 pin header which is a bit of a waste of a full slot, if I'd thought ahead whilst constructing the backplane then I may well have soldered in a separate small header just for this module.  

I started by soldering in the reset switch and DIP-14 socket as these were the lowest components on the board, the resistors sit upright and so are above the profile of these parts. One thing to watch if you are using a low profile crystal, is if it is soldered flush to the PCB it will foul the plastic portion of the header beneath it once you come to soldering that in place, so it is best to leave a gap of a few mm. 



After soldering the rest of the passives into place, I offered up the header and luckily I'd left plenty of room underneath the crystal for it to fit. It is rumoured that there may be a backplane PCB in development so hopefully the issue of one tiny module occupying a whole slot will be resolved, though the loss of flexibility brought by an easily removeable/replaceable clock may prove to be a disadvantage in the long run.

I have deliberately left fitting the logic into place 'till last in order to minimise the risk of electrostatic problems associated with sticky fingers :).