CFX

[Dave]

No problem, I do like it when people read my waffling - otherwise, there's no point in writing that stuff

I have not tried this, but if you really wanted CP/M AND the RS232 channels, you should be able to remove the FDX ROM from the RS232 board and run CP/M from the CFX

[stephen_usher]

I'll probably have to do that anyway as as soon as you run "ROM 5" it crashes to the PANEL. That's if the machine starts at all.

I can't actually see any ROMs. There's the Z80 DART, a bunch of 74LS chips, the PAL and three 75XXX chips and that's it.

[Dave]

That's ODD, the SDX ROM should run OK - assuming that all the other problems have been fixed now (?)

I can't recall, what RAM do you have in the machine now?
Have the links been set for the right memory size ?

I think you must have 64k if the CP/M ROM is running OK - is it?

Is everything else working now?

[stephen_usher]

64K RAM (TI chips). The LK6 links have been changed but LK7 hasn't. However, Andy's GAL code ignores that input anyway.

P.S. I can't try CP/M mode as the 'C' key is one of those which isn't operational until I get a replacement 74LS273, which probably arrives on Tuesday.

[Dave]

But it works fine when the RS232 board is not fitted?

[stephen_usher]

But it works fine when the RS232 board is not fitted?

Yep! Despite the keyboard issues I've managed to load "REV.RUN" and "KILO.RUN" (I can't load any .BAS or .MTX as the 'B' and 'M' keys are not functional.)

[Dave]

Mmm, that’s odd.

Martin, any ideas?

[stephen_usher]

But it works fine when the RS232 board is not fitted?

OK, I have found one issue. The machine's stable when in BASIC and running games.

The machine boots into the CFX menu fine and as long as you enter BASIC within about 10 seconds everything is fine. If I leave it any longer then the machine will reboot into the CFX menu or (very rarely) drop into the PANEL. This is consistent. It's almost as if the RAM refresh isn't happening. Wierd.

[Martin A]

Mmm, that’s odd.

Martin, any ideas?

The PAL on the RS232 is the usual 14L4. Looking at the pal-assem code for that in the phoenix manual:

• Pin 14 is the direction pin for the LS245 buffering the data bus

• Pin 15 enables the DART I/O ports, it's fully decoded so shouldn't clash with the CFX's I/O range

• Pin 16 seems to be a half of a paged rom select decode for either bank 4 or bank 5 (there's no R0 connection to the PAL or the external address decode), however with no FDX attached that shouldn't affect anything

• Pin 17 seems to be doing something with I/O addresses in the #20 to #FF range but the RS232 board schematic shows protection diodes so I don't think it can affect the rom select. However, it does feed back onto the GAL on pin 19, and that input is part of the LS245 direction control logic.

Memotech's original I/O map defined Ports #00 to #1F as internal to the MTX and #20 to #FF as external. The only thing I can think of is the RS232 PAL is doing something it shouldn't because of an assumption that all the External I/O is in the FDX.

The feedback between the output from pin 17 and how that affects the output at 14 could be the culprit. Maybe it's triggering the 245 into putting rubbish on the bus when the CFX is doing I/O. That would be enough to crash the MTX as soon as any CPM based functions are called, as the SDX code uses the CPM BDOS loaded off the CF, instead of having it's own disc handling routines.

It probably needs "someone" with an RS232 board to see if they can replicate the issue. If it can be duplicated, then it shouldn't be too hard to come up with a replacement for the RS232 PAL that excludes the CFX's I/O ports from the "external" range. The 16V8 has double the number of terms available when compared to the 14L4 so "tweaking" the equations for pin 17 is doable.

[Dave]

It probably needs "someone" with an RS232 board

I guess that means me?

Why don't you do it? - Oh, I know, maybe because I have your RS232 board

I'll try and see if I can duplicate the issue during the week