Search found 5196 matches

by 1024MAK
Wed Jun 19, 2024 10:53 am
Forum: ZX BASIC
Topic: Alternative to IN to read the keyboard on the zx81?
Replies: 5
Views: 58

Re: Alternative to IN to read the keyboard on the zx81?

A machine code program that reads a Z80 I/O port and returns the result to BASIC is in this post . In that post it's reading a joystick, but it should be easy enough to adapt it to read the keyboard directly. A BASIC program is never going to be fast enough to scan all forty keys. But it should do f...
by 1024MAK
Wed Jun 19, 2024 10:42 am
Forum: Development
Topic: Use of FAST mode... for typing?
Replies: 5
Views: 126

Re: Use of FAST mode... for typing?

It should also be noted that most modern TVs, including the later CRT models, also added 'no signal' detection. Then, when the display cannot detect a valid sync it switches to an internally generated 'no signal' picture. Rather confusingly, this 'feature' may work differently on different inputs of...
by 1024MAK
Wed Jun 19, 2024 8:06 am
Forum: Development
Topic: Use of FAST mode... for typing?
Replies: 5
Views: 126

Re: Use of FAST mode... for typing?

That's an effect of the automatic input selection (on the SCART) system. When the ZX81 was designed and manufactured, it was intended to be used with the CRT TV's of the day. Which typically only had an aerial input socket. Even when TV's started to get SCART sockets, they mostly had manual input se...
by 1024MAK
Tue Jun 18, 2024 3:05 pm
Forum: Hardware
Topic: sinclair spectrum eprom swap gone wrong
Replies: 15
Views: 983

Re: sinclair spectrum eprom swap gone wrong

Not sure what's going on with the 7805 0V/GND Pin :shock: Has a 0V/GND line been broken somewhere? That kind of fault sometimes can cause a 0V/GND to float up via leakage from the +5V rail. One end (the links side) of R33 also goes to the expansion/edge-connector (25 lower, signal called /ROMCS). Ex...
by 1024MAK
Tue Jun 18, 2024 1:48 pm
Forum: Hardware
Topic: Paper for Alphacom 32 / TS2040 on AliExpress
Replies: 4
Views: 224

Re: Paper for Alphacom 32 / TS2040 on AliExpress

Alphacom 32 print-out
Alphacom 32 print-out
As Moggy says, the paper from www.shopstuff.co.uk is good. This print-out has been printed on a roll from this supplier.

If anyone from the UK wants one or two rolls, I can sell them at cost price plus the cost of postage and packaging.

Mark
by 1024MAK
Mon Jun 17, 2024 12:07 pm
Forum: Hardware
Topic: sinclair spectrum eprom swap gone wrong
Replies: 15
Views: 983

ZX Spectrum 16K/48K ROM socket

ZX Spectrum 16K/48K ROM socket Pin Function Destination 1 N/C 2 A12 Z80 pin 2 3 A7 Z80 pin 37 4 A6 Z80 pin 36 5 A5 Z80 pin 35 6 A4 Z80 pin 34 7 A3 Z80 pin 33 8 A2 Z80 pin 32 9 A1 Z80 pin 31 10 A0 Z80 pin 30 11 D0 Z80 pin 14 12 D1 Z80 pin 15 13 D2 Z80 pin 12 14 0V/GND 15 D3 Z80 pin 8 16 D4 Z80 pin 7...
by 1024MAK
Mon Jun 17, 2024 11:12 am
Forum: Spectrum BASIC
Topic: Quick hardware check with Peek
Replies: 2
Views: 83

Re: Quick hardware check with Peek

PRINT PEEK 23732 + PEEK 23733 * 256 returns the address of the top of available memory available to BASIC by using a system variable. The BASIC ROM does a test to discover how much RAM is available. PEEK 23733 returns the most significant 8 bits of the address (address lines A8 to A15). In both case...
by 1024MAK
Sat Jun 15, 2024 2:53 pm
Forum: Hardware
Topic: TS1000 Diagnostic Help
Replies: 14
Views: 394

Re: TS1000 Diagnostic Help

Yes, a problem with the market in programmable logic chips is that most 5V or 5V tolerant devices have been discontinued. The main market is now 3.3V devices. To use with 5V TTL (such as the ZX81) means using level shifter chips or finding and adapting the design for one of the 5V or 5V tolerant dev...
by 1024MAK
Sat Jun 15, 2024 12:25 pm
Forum: Hardware
Topic: TS1000 Diagnostic Help
Replies: 14
Views: 394

Re: TS1000 Diagnostic Help

Question: apart from the ULA/vLA81, are any of the other chips in sockets? Do you have another TS1000 or ZX81? If yes, which chips (if any) are in sockets? Do you have any other computers based on / using a Z80A? Do you have an electronic breadboard, some modern LEDs, thin solid core wire (off cuts ...
by 1024MAK
Fri Jun 14, 2024 7:05 pm
Forum: Hardware
Topic: TS1000 Diagnostic Help
Replies: 14
Views: 394

Re: TS1000 Diagnostic Help

All the control signals are active low, including /INT, /NMI, and /HALT. Hence their normal inactive state is logic high. With all waveforms in a digital computer, the edges (rise and fall) will not be nice and clean due to stray capacitance, stray inductance, limitations with the output drivers in ...