Search found 546 matches

by 1024MAK
15 May 2019 17:28
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

0x55 and 0xAA are however useful to check if there are any cross connections between adjacent data bus lines ;) They are also useful for when you are testing 4 bit DRAM chips, or when testing SRAM chips... I agree with Dave, if using BASIC, forget using an array, use POKE and PEEK instead. Just watc...
by 1024MAK
15 May 2019 08:21
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

I'm guessing the diag ROM merely writes and then reads, which will only detect one type of error. The daig rom writes an XOR of the high and low bytes of the address to each location as it fills the memory, then reads back to check the correct value is present. The early version wrote a fixed patte...
by 1024MAK
11 May 2019 23:15
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

That’s good progress :D

Is the power on reset circuit working okay? It’s formed by R18, D13 and C11 (10uF) on the input to IC 9C (4070B).

Mark
by 1024MAK
11 May 2019 21:51
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

You can also use HM4816 or equivalent DRAM chips...

Mark
by 1024MAK
11 May 2019 10:48
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

You can also feed the Y output from J12 pin 2 to a composite monitor or SCART TV. The signal needs to go through a resistor to form a voltage divider as the 9929 outputs a nominal 3v peak voltage, and composite 1v (on SCART at least) 470R is the resistor value I found "on the net". That to me seems...
by 1024MAK
11 May 2019 02:13
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

With the PAL video board, if using the baseband / composite video output, you can by-pass the LM1889 by removing link 'a' and fitting link 'b'. You should then get a monochrome video output. Note that C52 is deleted and replaced with C63, 100uF 16V or 25V (I recommend 25V). Note that C51 is deleted ...
by 1024MAK
11 May 2019 01:43
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

8k ROM decode for Z80 CPU using a single 74xx138
8k ROM decode for Z80 CPU using a single 74xx138.png
8k ROM decode for Z80 CPU using a single 74xx138
8k ROM decode for Z80 CPU using a single 74xx138.png (37.21 KiB) Viewed 27 times
Mark
by 1024MAK
11 May 2019 00:52
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

8k ROM decode for Z80 CPU using a single 74xx32 8k ROM decode for Z80 CPU using a single 74xx32.png While you were taking measurements, I drew this in case it helps. It only decodes the one 8k ROM. So use it in addition to the GAL/PAL and replace the ROM CS with the output of this circuit (use a tes...
by 1024MAK
10 May 2019 23:48
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 210
Views: 1739

Re: Resurrecting an MTX500.

What is the state of the other inputs to the GAL/PAL (6A)?

Mark