CFXII - Black screen with it plugged in

About original Memotech hardware.
acsi
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Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

OK so the Caps arrived today and promptly got swapped and the missing C53 fitted.

Apart from the display looking more stable (may just be me) the CFXII still does not work. I may have to try and find someone in NZ with an MTX to test the CFX out as that would identify if its the MTX or the CFX.
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

I’d be happy to test it for you, obviously, the return postage cost to the UK isn’t trivial, but the offer is there if you need it

Regards
Dave
acsi
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Re: CFXII - Black screen with it plugged in

Post by acsi »

Thanks Dave, I'm also not sure about any VAT or GST impacts.

In the meantime the sound issue I also have is making me wonder if the issue isn't something on the MTX itself. I've ordered a replacement PSG and have socketed the exisiting one. Once that arrives if the sound works then I think it'll be just a coincidence in timing and the CFX is probably faulty.

Will let you know how I get on.

Thanks
Mike
Martin A
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Joined: 09 Nov 2013 21:03

Re: CFXII - Black screen with it plugged in

Post by Martin A »

I've been playing around with the CFX-2 here, and I've a couple of things you can try.

If you remove the ROM from the CFX-2 board the propeller will start up in test card mode. All that needs is a working power supply it should display even if the MTX is locked
Test card mode
Test card mode
prop boot.jpg (110.36 KiB) Viewed 9523 times
If the MTX boots and the propeller has also booted the you can send data to the 80 column display with OUT 96,x
Simple as ABC
Simple as ABC
code.jpg (65.46 KiB) Viewed 9523 times
Poor quality, sorry!
Poor quality, sorry!
direct access.jpg (47.68 KiB) Viewed 9523 times
IF that all works, there's one more test to try with the ROM back in.

Try RESET-C to force a CPM mode start up.

If CPM stars sucessfully, and you have access to a chip programmer, you could try re-programming the rom with the attached rom build. It's got some code to force a reset of the propeller on every boot (and not just the 80 mode boot to CPM). If it works it will report as build 281.

This fixes something I spotted whilst playing with the board, but it needs a working sound chip to be sure if it's needed! I found there were certain conditions where the MTX would play the CFX start up chimes and then be unresponsive with a black screen. The software reset of the propeller cures that.
Attachments
CFX2ROM,280.zip
New Build
(9.24 KiB) Downloaded 377 times
acsi
Posts: 69
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

OK so with the ROM chip removed I still get no signal from the CFX so would I be correct in suspecting the Propeller chip?

With the ROM removed I do get the Ready prompt and cursor through the composite output. With the ROM in place I just get a black screen through the composite output and no signal through the VGA.

Can I just replace the propeller chip or does it need programming?
Martin A
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Joined: 09 Nov 2013 21:03

Re: CFXII - Black screen with it plugged in

Post by Martin A »

The propeller has a small bootloader built in, and that reads the contents of the 8 pin Serial ROM (24LC256) for the main VGA driver code.

NB: Being a serial rom it's quite "slow" in computer terms and back when I wrote it put I a coment in the z80 boot code say it takes 1.35 sec for the propeller to boot.

IF either the propeller or the serial rom the issue (or U5 the 3.3v regulator come to think of it) then the MTX would boot, play the start up tune, and then lock up waiting for the propeller to initialise. Combined with a non-functioning sound system, that would explain the symptoms.

I've run some tests faking a propeller issue (by removing the serial rom that's easier to pull!) normal boot black screens after the tones as expected. Reset with C held down will produce a blue screen and "CPM boot" and then lock. Reset M for MTX mode produces a normal boot. With the propeller disbled the VGA mointor reported no signal the whole time I was testing.

The Normal MTX boot up is:
Quick and diry test for paged ram
Check for an initialise autoboot roms
Setup the PSG and VDP.

The key thing to note from that is that the normal boot sequence has done nothing with either the PSG or VDP before it calls the boot roms.

With a CFX-2 fitted there are 2 auto-boot rom images in the flash chip.
  • The rom in slot 4, the CPM rom gets the first try, that checks for the C key, then starts the Propeller in 80 column mode and runs CPM boot process if it's pressed
  • The rom in slot 5 is next, the SDX rom, that checks for the M key or space key (magrom mode) and starts propeller in 40 column mode and initialises the the basic extensions if neither key is pressed.
All of the paged boot rom checks occur "long" before the Propeller finishes booting so both need to wait at some point. The CPM rom sets up the VDP while it's waiting, as it's basically free CPU cycles, and once the CPM boot message is printed the VDP is ignored.

The SDX rom however, if it's taking conrol, has to request and wait for the propeller's 40 column mode to initialise before setting up the VDP. It's done that way so that the VDP shadowing works.

Thats why reset-C produces a blue screen and normal reset doesn't. So, the test at this point might be to test both reset-C and reset-M with the board connected and ROM plugged in, and see what happens.

If reset-M gets to the basic prompt then both the boot rom and the CPLD are doing what they should and something in the propeller subsystem is the likely culpit.

NB2: The Silicon disc if fitted can be tested from basic with:

Code: Select all

10 FOR X=1 TO 20
20 PRINT INP(83)
30 NEXT
If that prints anything other than 120 on every line the CPLD is probably paging that correctly too.
acsi
Posts: 69
Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

U5 the 3.3v regulator


U5 gives 3.3v
I've run some tests faking a propeller issue (by removing the serial rom that's easier to pull!) normal boot black screens after the tones as expected. Reset with C held down will produce a blue screen and "CPM boot" and then lock. Reset M for MTX mode produces a normal boot. With the propeller disbled the VGA mointor reported no signal the whole time I was testing.
So, the test at this point might be to test both reset-C and reset-M with the board connected and ROM plugged in, and see what happens.
With the serial ROM removed I get a black screen through the composite output and after Reset - C I get a blue screen with "CPM Boot" displayed, Reset - M gives a blue screen with the ready prompt.
NB2: The Silicon disc if fitted can be tested from basic with:
CODE: SELECT ALL
10 FOR X=1 TO 20
20 PRINT INP(83)
30 NEXT
If that prints anything other than 120 on every line the CPLD is probably paging that correctly too.
Gives 20 different numbers (apparently random? if run again they change)

So I gather the issue at hand is either the Propeller chip or the Serial Rom.

I have put the serial rom in my programmer and verified it against the MTX_Monitor_10 file. It gets about half way then errors. But then according to the list my CFX came with monitor 10A? I cannot seem to find a download for Version 10A?

Should I try reprogram the eprom with version 11?
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

There is an inconsistency in how the EPROM versions are named, the 171112 on the webpage file is the 10A version

The one on the website under that name is what you have loaded, but Version 11 should be fine too if you want to upgrade, though you should also upgrade the ROM too if you change the Propeller code version

regards
Dave

p.s., Martin also reminded me that I had to use a patch wire to correct a power connection problem on the board. There should be a very short patch wire (1.5cm) on the CFX-II board behind the EPROM socket that is needed to provide power to the EPROM. For the internal version, with CFX-II installed, you should see it at the top left corner. You should check that it has not become damaged/detached.
acsi
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Joined: 16 May 2019 08:49

Re: CFXII - Black screen with it plugged in

Post by acsi »

Thanks, I've erased the rom and written that version to it.

No change unfortunately. Maybe the propeller chip needs replacing? I can source a replacement through RS Components is it just a straight swap?
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Dave
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Re: CFXII - Black screen with it plugged in

Post by Dave »

Did you check the power patch wire?

Yes, the Propeller can just be swapped out if needed

regards
Dave
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