Sinclair ZX80 / ZX81 / Z88 Forums

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

IR=$1E00 R= %000* 0000 (*) Where the bit B4 is set to 1. 000* 0000 "(" 000* 0001 ")" 000* 0010 ">" 000* 0011 "<" 000* 0100 "=" 000* 0101 "+" 000* 0110 "-" 000* 0111 "*" 000* 1000 "/" 000* 1001 ";" 000* 1010 "," 000* 1011 "." 000* 1100 "0" 000* 1101 "1" 000* 1110 "2" 0001 1111 "3" 0001 0000 "(" 0001...

bad connection on the alternative address lines from the ULA ? if everything else appears to be working then no fault on data lines or adderess lines from cpu to rom / ram. try doing this 10 for t=0 to 63 20 print chr$(t); 30 next t and run it.... or just type "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" ...

My UDG arrived quickly (thanks Andy!) and just go this up and running at lunch time. Amazing stuff! Really impressive and a great way to showcase what the humble zeddy can do. 8-) LOL reminded me i hadn't even marked it as sent nor entered the tracking number on paypal :lol: Glad it arrived quickly...

Moggy wrote: ↑Sat Aug 24, 2019 9:08 pm This is superb work and I cannot wait for the encoder to see the light of day as I will have some serious fun with that.

Do we need to ask the admin for a password protected 18+ area

WOW i am blown away... Fabulous work, this is truly amazing something that was only a dream before today full screen hi-res ( of sorts ) full speed video on ZX81... ARE YOU FREAKING KIDDING ME !!!! Damn this should win some sort of award. Running on real hardware B+W CRT monitor viewed from 6 or 7 f...

Hi..... the link puts a 75 Ohm load resistor into across the output path. it is meant for oddball monitors that have hi impedance inputs. i highly doubt that any damage could occur if the link is set wrong. you most likely will get a wobbly image. as the monitor will not be able to "lock" onto the s...

Yes they went rather faster than i expected... will have more soon.

I've ordered one of Charley Ingleys ULA looks like a fabulous bit of kit.

Regards Andy