Sinclair ZX80 / ZX81 Forums

When we reach the RET of routine keyboard HL will be something of the following 1 - 2 - 3 - 4 - 5 -> register L = F7 0 - 9 - 8 - 7 - 6 -> register L = EF Q - W - E - R - T -> register L = FB P - O - I - U - Y -> register L = DF A - S - D - F - G -> register L = FD N/L- L - K - J - H -> register L = ...

Welcome to the Forum, Lots of love for the humble machine. you can really do alot with it.

any questions just ask away.

Regard Andy

I've seen similar on zx81 isue 3 boards with red solder mask but in my case they were 1K resistors

Andy

put the sd in after powering on and see if it is recognised do a CAT

awesome that preview looks really smooth, will download and try on real hardware... BOBS played with ray traced texture mapping in lo-res a long time ago... https://www.sinclairzxworld.com/viewtopic.php?f=4&t=548&p=4951&hilit=3d+rendering#p4951 the facebook video link https://www.facebook.com/bobs.s...

Nice Trick, Thanks for sharing...

Andy

yes JR 4 bits lol nope..

JR and index offsets both 8bit SIGNED

quoted instead of edit sorry

haha your right the IX and IY registers can't be negative but for example say they are holding the value $0000 and you add a negative offset it will roll round to $ffff for -1 $fffe for -2 $fffd fro -3 and so on... btw LD IY,-20000 ; is perfectly valid and results in the following bytes DD 21 E0 B1 ...

when using the index registers the offset byte is signed so -128 to +127 is the maximum range allowed.

same as relative jumps.

tasm allows you to enter negative numbers.

regards Andy