Re: MK14 schematic revisions
Ordinarily if you just strap a few control lines into certain states power it up and you have, oh, provided it with a clock the VDU will just display whatever nonsense it is seeing on the unterminated data lines. Did you remember to pick up the clock from the underside of the issue VI PCB? If not, the clock input on the VDU will be shorted to 0V at present.
Of the control lines the most important would be b13 'VDU OFF', which disables the VDU when high and enables it when low according to the manual.
On the PIC 'VDU driver' PCB I have b13 [Blank screen / VDU OFF] is just tied permanently low so the VDU is enabled, but when used with an actual system it will need to start off disabled because it has a very big effect on the system speed and none of the current loading methods (cassette, uploader etc) will work when it is enabled because the system is constantly being halted while the VDU reads data from its RAM.
What's therefore needed is a modest pullup on B13 which will hold the VDU -off- until such time as the user intentionally switches the 8154 PA0 output from input to output and then drives it low to turn on the VDU.
A reminder, attached, of how the MK14 top side and VDU 'b' row connections line up if they are connected together one-to one. b27 (Clock into VDU) and B15 (reverse pages) are the main ones which need sorting out.
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