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SiriusHardware · 26th Sep 2022, 5:20 pm

Thanks for the prompt action, Colin - yours is more like we would ideally expect, all of SD0-SD7 comfortably low except for SD5, which we would expect to be high. Thanks for also taking the time to do the outputs of UF9, where again there is one bit high, seven low as expected.

Just caught BrackenFix's UF9 measurements and there we can see that the 1.1V coming from the SD4 line is being converted to a logic '1' by the time it comes out through the other side of UF9, and this perfectly explains why all the character codes are being modified by +10 (hex) before they go to the character generator ROM which I believe we can now rule out.

BrackenFix, do you have any low value resistors, around 470R or thereabouts?

26th Sep 2022, 5:20 pm	#96
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,560	Re: 1978 Commodore PET project Thanks for the prompt action, Colin - yours is more like we would ideally expect, all of SD0-SD7 comfortably low except for SD5, which we would expect to be high. Thanks for also taking the time to do the outputs of UF9, where again there is one bit high, seven low as expected. Just caught BrackenFix's UF9 measurements and there we can see that the 1.1V coming from the SD4 line is being converted to a logic '1' by the time it comes out through the other side of UF9, and this perfectly explains why all the character codes are being modified by +10 (hex) before they go to the character generator ROM which I believe we can now rule out. BrackenFix, do you have any low value resistors, around 470R or thereabouts? Last edited by SiriusHardware; 26th Sep 2022 at 5:31 pm.