Thread: Mk14 vdu
View Single Post
Old 4th Jun 2020, 12:20 am   #38
Timbucus
Octode
 
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
Default Re: Mk14 vdu

Just a word of caution - try testing the voltages after the VDU is hooked up on the expansion bus on PA0-PA7 BEFORE you plug in the 8154 - I was getting readings around 6v and could not control text/graphics mode using PA6 by writing bits to it after setting it to an output port. Maybe we have to sink too much using the IO/chip alone if they are normally high - some study needed of the circuit I think.

It might be worth on your little conversion device having a set of links that can be made or broken for each PA0 connection - I need to look into what is happening - hoping I have not done any damage to my only 8154! The eliminator will be back in for the moment.

I have also found a flaw in our 1:1 mapping - hooking the "top page" line b17 to PB0 as an input is great to sense in software (in theory) when you are there but, you also need to link it over to b11 on PA1 so that the VDU board auto swaps the memory page to display both pages - that cannot be done fast enough in software.

I started down this road typing the Charset demo from the manual which 'only' needs the I/O chip to execute from so though what the hell and plugged it in and started using your trick of just writing to the 0800 areas after setting 0822 to 1...

I did this as Sirius asked if the char set was the same. Anyway more updates later in the week.

Actually I am getting high readings >7v on SIN and SENSE_A and other lines when my VDU is hooked up with no INS8154 - I wonder if something is coming back in that should not... I will have to take a serious look at the connections - especially if it is coming through the SC/MP!
Timbucus is offline