Search found 3778 matches

by 1024MAK
Sat Sep 25, 2021 7:48 pm
Forum: Spectrum BASIC
Topic: Bitwise AND
Replies: 2
Views: 244

Re: Bitwise AND

On a ZX Spectrum the logical operators AND, OR and NOT treat any non zero number as true. They are not bitewise. Note that these logical operators don’t necessarily return 1 for true, sometimes they return one of the arguments. Here is a ZX81 program showing how they work. It’s similar for the ZX Sp...
by 1024MAK
Tue Sep 21, 2021 11:11 pm
Forum: Hardware
Topic: ZX Spectrum issue 2 12v low missing bits of copyright logo
Replies: 1
Views: 172

Re: ZX Spectrum issue 2 12v low missing bits of copyright logo

The most important supply rail as far as the ‘lower’ RAM (made up of 4116 or equivalent DRAM chips) is concerned is the -5V rail. If this is out of specification (-5.5V to -4V) or missing then there is a problem with TR4 (and maybe a problem with TR5). You can check the -5V rail on pin 1 on IC6. See...
by 1024MAK
Sun Sep 19, 2021 8:23 pm
Forum: Hardware
Topic: Spectrum error
Replies: 16
Views: 962

Re: Spectrum error

Although given the price and that it’s marked as a 20MHz part, it may well be a relabelled 4MHz NMOS type! If you have a large electronic parts supplier in your country, it may be possible to get a brand new recent production part. Yes, CMOS Z80s are still in active production. Look for a Z84C0006PE...
by 1024MAK
Sat Sep 18, 2021 8:25 pm
Forum: Hardware
Topic: Spectrum - building a 48K issue 3B from scratch
Replies: 2
Views: 53

Re: Spectrum - building a 48K issue 3B from scratch

With no 4116 or equivalent ‘lower’ RAM, when the ULA tries to read screen data, it will instead read garbage. Whatever random voltages happen to be visible to the ULA on it’s data bus pins. So the ‘paper’ area of the display will be filled with constantly random colours and pixels. This assumes that...
by 1024MAK
Fri Sep 17, 2021 10:36 pm
Forum: Hardware
Topic: Harlequin 128K 2D not showing any video signal
Replies: 4
Views: 283

Re: Harlequin 128K 2D not showing any video signal

I’ve moved your post to the Sinclair ZX Spectrum Hardware section.

Mark
by 1024MAK
Thu Sep 16, 2021 10:01 pm
Forum: Sinclair Misc
Topic: R.I.P Sir Clive.
Replies: 20
Views: 1030

Re: R.I.P Sir Clive.

Yes, very sad news :(

May he enjoy the inventors heaven.

Mark
by 1024MAK
Wed Sep 15, 2021 10:06 am
Forum: Hardware
Topic: Noisy Spectrum...
Replies: 6
Views: 378

Re: Noisy Spectrum...

I wonder if should I ad bigger capacitors at C28 and C75? Keep in mind the ULA has two supply inputs. Pin 13 is the supply for all the matrix logic cells. Pin 14 is the 5V supply for the interface/peripheral cells that connect between the matrix logic cells and the pins. Also, what type of PSU are ...
by 1024MAK
Tue Sep 14, 2021 7:59 am
Forum: Hardware
Topic: Noisy Spectrum...
Replies: 6
Views: 378

Re: Noisy Spectrum...

Digital computers are electrically very noisy. This is due to multiple transistors inside the various chips switching on or off at multiple different rates. This is why there are so many (decoupling) capacitors used (modern rule of thumb is at least one per chip). Because the switching on/off (espec...
by 1024MAK
Mon Sep 13, 2021 8:31 pm
Forum: Hardware
Topic: Spectrum error
Replies: 16
Views: 962

Re: Spectrum error

Hello! I found a z80 from China on eBay. https://www.ebay.com/itm/311081981813?hash=item486dee5775:g:Pc4AAOSw7K1ep1kr That’s not a CPU, it’s Zilog’s serial UART. This site lists the various part numbers used by Zilog. You can also use a NEC D780C-1 CPU ( more details ). This is an equivalent and wa...
by 1024MAK
Mon Sep 13, 2021 7:05 pm
Forum: Software
Topic: Block save / load
Replies: 15
Views: 1967

Re: Block save / load

Thanks :D

Oh, by the way, we now know that there were three ROM versions!

Mark