Quote:
Originally Posted by Timbucus
in Issue 5 the review of the VDU suggests hooking up B13 to Flag 1 , B14 to Flag 2 and B16 to flag 0 - so we are breaking canon! Using the IO chip is better though I think.
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The original instructions for the VDU say to do that (use the Flag outputs), otherwise it would have excluded people who did not have a RAM I/O fitted - bearing in mind that the RAM I/O was an option, not standard.
People generally did not use a 'hard' one to one connection between the VDU and the MK14, so they were able to choose which flags or I/O lines to connect for these purposes.
One minor problem I forsee (I have not thought it through, but...) you will want the VDU to be disabled on MK14 reset, because when it is enabled it constantly halts the CPU and drags the overall system speed right down, meaning that the cassette interface or any scheme which uses it indirectly (ie, Serial download from PC as per Karen O's idea) and for that matter the Pi uploader will not work, unless of course you slow the latter down to the speed of mud.
The I/O device I/O ports start off in high impedance input mode so a pull up or pull down resistor (can't remember which) will be needed on the 'display blank' connection to hold the VDU off until such time as the user puts that I/O port pin into output mode and intentionally turns the VDU on.