Search found 430 matches

by Martin A
30 May 2019 19:05
Forum: OFF TOPIC
Topic: Homebrew DIY SAM Coupe ?
Replies: 16
Views: 2223

Re: Homebrew DIY SAM Coupe ?

If you're building a system that can't use PS2 or USB, then the cost of the keyboard components is possibly the biggest outlay. Buying from Mouser in packs of 100, a 12mm key and keycap works out at 60.6p each. With anywhere between 40 (ZX81, Spectrum) and 80 (MTX/MSX/SAM) in a home brew, that can b...
by Martin A
25 May 2019 22:21
Forum: NEW HARDWARE
Topic: System test rom/Board
Replies: 26
Views: 3000

Re: System test rom/Board

The memory test could be re-written to stop at a failed read back, and then print something along the lines of "Value read :XX value expected :XX". at which point the test would have to stop. I don't think there's enough registers to do much more than that. Re-starting and only halting once the scre...
by Martin A
20 May 2019 19:03
Forum: MEMOFEST 2019
Topic: A bit early.
Replies: 7
Views: 947

Re: A bit early.

Crazyboss wrote:
20 May 2019 15:32
If its Cambridge, I looks like there is an airport nearby, but its seems like its closed, at least its not possible to fly there from Copenhagen :)
Try flights to and from London Stanstead - that's got a direct train to Cambridge, takes about half an hour according to the time table.
by Martin A
18 May 2019 20:54
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18241

Re: Resurrecting an MTX500.

I only mentioned the TIP as that was a problem with one of my MTXs. I spent 2 weeks chasing a "timing problem" of random crashing and inability to run programs for any length of time, which turned out to be nothing to do with the timing. Anyway, if the big 10R resistor R62 next to rom B isn't hot th...
by Martin A
18 May 2019 09:58
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18241

Re: Resurrecting an MTX500.

Silly question, did you replace the TIP2955 in the power regulation section ?

(20 pages of thread is a lot to re-read, so I'll just ask instead :oops: )
by Martin A
16 May 2019 20:39
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18241

Re: Resurrecting an MTX500.

I've used the 10mhz CMOS Z80 (Z84C0010PEG) in my MTX's for years, with no issues. In fact we found out it works better with the CFX2 than the NMOS version. The only reason one of them has the NMOS chip back in it is for testing. As Dave says we've found a lot of fakes marked up as the 20mhz part (Z8...
by Martin A
16 May 2019 17:49
Forum: INTRODUCE YOURSELF
Topic: Hello
Replies: 13
Views: 1423

Re: Hello

One advantage of de-soldering rather than clipping legs is, if the 32k onboard is made up of the 3732H part, you potentially have replacements for the video ram. The trick for replacing a 4116 with a 4164 ties A7 high to reduce the chip to 16k x1 which would in theory work on the high bank 32k chips...
by Martin A
16 May 2019 16:59
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18241

Re: Resurrecting an MTX500.

Something to consider, the RUN type games usually load and run at #8100. REV.RUN is 14k in size so fits entirely into the paged memory area between 8000 and BFFF STAR.RUN is 18k in size so overflows into the unpaged memory at C000 onwards CPM has all of it's drivers in the top 4k of the unpaged area...
by Martin A
15 May 2019 20:47
Forum: NEW HARDWARE
Topic: CFX
Replies: 56
Views: 10512

Re: CFX

If I'm reading the schematic for the RS232 board correctly, Rom decode for the FDX is potentially as much of a problem as the I/O port decode. Whist the DART is compatible with the CFX it looks like the communications part of the board isn't. So I've come up with a GAL design that enables just the D...
by Martin A
14 May 2019 23:35
Forum: HARDWARE
Topic: Resurrecting an MTX500.
Replies: 226
Views: 18241

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...