Search found 2997 matches

by 1024MAK
Fri Jul 10, 2020 11:18 pm
Forum: Hardware
Topic: A tale of 2 Spectrums...
Replies: 5
Views: 61

Re: A tale of 2 Spectrums...

I THEN decided to check at IC6 and got 8v at ground ! Measured again and got 0v, measured again and got 7.6 and rising, then 0v again Now I just need to figure out WHY ! I suspect a faulty ram module leaking volts to ground ? Hmm, what point are you using for the negative lead (black probe) for you...
by 1024MAK
Fri Jul 10, 2020 6:09 pm
Forum: Development
Topic: ZX81 Assembly on OSX
Replies: 13
Views: 143

Re: ZX81 Assembly on OSX

wietze wrote:
Fri Jul 10, 2020 4:39 pm
Would you be able to point me to some more in depth resources regarding this?
Read Wilf Rigter’s Video Tutorial first ;)

Note: by default the pages at the linked to web site may not display correctly, so switch your character set to "western" for correct display.

Mark
by 1024MAK
Fri Jul 10, 2020 3:06 pm
Forum: Development
Topic: ZX81 Assembly on OSX
Replies: 13
Views: 143

Re: ZX81 Assembly on OSX

It maybe worthwhile mentioning that a user program (BASIC or machine code) will only run at the maximum MPU speed if the machine is not generating a display, this is known as FAST mode. This is the same as the system used by the ZX80. The normal ZX81 mode is SLOW mode, also known as compute and disp...
by 1024MAK
Thu Jul 09, 2020 10:47 pm
Forum: Hardware
Topic: ISSUE 2 - memory problem
Replies: 4
Views: 71

Re: ISSUE 2 - memory problem

Oh, since I forgot to welcome you, let me do that now...

Welcome on board Rob!

:D :D :D

Welcome to Sinclair ZX World :D

Mark
by 1024MAK
Thu Jul 09, 2020 10:46 pm
Forum: Hardware
Topic: A tale of 2 Spectrums...
Replies: 5
Views: 61

Re: A tale of 2 Spectrums...

Oh, my bad, I forgot to welcome you :oops:

Time for me to correct that, so...

Welcome on board JetSetWally!

:D :D :D

Welcome to Sinclair ZX World :D

Mark
by 1024MAK
Thu Jul 09, 2020 10:29 pm
Forum: Hardware
Topic: A tale of 2 Spectrums...
Replies: 5
Views: 61

Re: A tale of 2 Spectrums...

I don’t recommend testing ULA pin 39. If the ULA produces a video picture, then the 14MHz oscillator is running. If you want to see that the ULA is working, test the Z80 clock signal on pin 6 on the Z80. But note that it may vary slightly as the ULA contention to the Z80 is applied via the CPU clock...
by 1024MAK
Thu Jul 09, 2020 9:26 pm
Forum: Hardware
Topic: ISSUE 2 - memory problem
Replies: 4
Views: 71

Re: ISSUE 2 - memory problem

Do you mean A15 on the edge-connector / expansion port? A15 comes from directly from the Z80. The BASIC POKE command and the PEEK function can access the whole 64k memory map regardless of anything else (if the upper RAM is disabled it obviously will ignore any accesses). Hence A15 will go high when...
by 1024MAK
Thu Jul 09, 2020 1:26 pm
Forum: Hardware
Topic: ISSUE 2 - memory problem
Replies: 4
Views: 71

Re: ISSUE 2 - memory problem

When you say black square, do you mean that the border is white and the the whole of the text and graphics area is black? The ROM code does not do a RAM functional test as such. The objective of the ROM test is to work out how much RAM is fitted. During the test, you should see thin vertical red lin...
by 1024MAK
Wed Jul 08, 2020 12:34 pm
Forum: Hardware
Topic: Differentuating a different logic states/pulses on oscilloscope
Replies: 14
Views: 615

Re: Differentuating a different logic states/pulses on oscilloscope

At some point, I’ll split out the relevant posts into a new topic.

Mark
by 1024MAK
Mon Jul 06, 2020 8:47 pm
Forum: Hardware
Topic: Differentuating a different logic states/pulses on oscilloscope
Replies: 14
Views: 615

Re: Differentuating a different logic states/pulses on oscilloscope

In a Z80 based system, the control lines are essential. They are like the command structure in a military operation. They control and keep order and keep everything in step. The main control lines are: /MREQ - (memory request) used by the Z80 to signal that the current cycle is a memory cycle and th...