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Construction

To the left we have the rudimentary single 8 bit  inport as used for the clock. As you can see, FIVE �bits� of the eight are used for the display setting switches, TWO are spare and the eighth is used for the 50Hz timebase input. ( 60Hz if you are in the USA of course! ) Note the inclusion of a very simple switch debounce circuit and the CPU connections via a 74xx32 OR gate and 74xx14 inverter.

Click on the above icon to show a diagramatic flow chart of how we can use a software clock with NO subroutines.

Software

Projects

8085 page

Fault Finding

Data Sheets

Programmer

To the left we have the top and bottom board layouts for the �universal� Z80 processor card. Far from being really universal, it is somewhat  limiting in it�s depicted state. Note that although the layout includes a 2K RAM, it is a �skinny DIP� variety. If using a 6116 or larger variant, remember to allow for more room on the board. The two IDC type headers need not be on the board either, which will free up some space for perhaps the system clock circuit or oscillator module? Remember that the 74xx139 is a dual decoder so the unused half can be used for expanding the I/O if desired.

Of course the family can be changed to all HC devices in place of the specified LS.

Note that the parallel lines on the underside layout are the suggested positioning for the wiring combs.

VIDEO info

Peripheral circuitry

Z280 and  Central Heating  Controllers

Concluding ideas

Links

http://www.hampshire-shops.co.uk

Click on the drawing to the right to show a full sized image of the �universal processor� that we use as the basis for the digital clock.