exxos's Atari, Amiga & retro forum

Perfect! Thanks for all your help.

I think I found an issue, but I want to confirm before I solder a bodge wire.

Pin 45 is the IACK pin on the MFP, and it looks like the GST should signal to the MFP it got the interrupt request, and I assume at that point will then pass the vector info on the buss for the GST or 68000 to interpret then proceed.

Anyways using the wonderful schematics here https://easyeda.com/editor#id=e4596c34d ... 207a38e830 , I have confirmed I do not get a connection from pin 83 on the GST, to the MFP!

I can tone out the VIA in a cluster of 3 to the MFP to the upper right of the GST, but that line continues under the board to a VIA below the GST, then connects under the GST on top to the Pin 83.

Anyone with a working STE and a board like mine, can you confirm if Pin 45 on the MFP U203 does indeed tone out to pin 83 on the GST U400? If so I will bodge it! I assume a corroded via or trace.

I think you opened a can of worms there.. I tried on 2 STE's and IACK has no connection from the MFP pin 45 to anywhere on the GST :shrug:

Darn, was hoping it would be easy, but previous experience tells me schematics have errors. Weird.

Guess the MFP is coming out next. Stay tuned...

So I dug for a few minutes on the internet, looks like all these later ste service manuals are based off the original 1989 docs, when the gst and blitter I think were separated. The 1989 docs that still have hand drawn schematics show the ack pins for the gst and mcp connected. Does anyone have schematics for the Revision C board.

I think people trying to be helpful merged info together...

I assume during chip reduction by Atari minimal cost changes were done do get it all on the one chip and some lines are dead ends on the board or connections through a via.

exxos wrote: 09 Dec 2022 22:09
Pin 32 will always be low because ( I assume) you are using a mono monitor ? But also the GST has to request the data from the MFP so the GST IPLx pins should not be low all the time.

Pin 52 is the MPF_CS line which is driven by the GST.. That should not be low all the time.. *unless* it never gets DTACK from the MFP. If both are low then the GST is stuck on that access for some reason. In which case, BERR will be triggered on the CPU.

This is with no monitor or adapter connected, what would cause the mono pin to be triggered with nothing connected? I have to verify this. When I do hook a monitor up I am only using one of your dongles I bought years ago with a soft switch for hires, low res over vga port. I did noticed on power up it goes hires and on pressing the STEs reset the screen switches to low res. My lcd handles both.

I will check pin 52.

Ignore my pin numbers , I was looking at the PLCC MFP.

exxos wrote: 10 Dec 2022 00:41 Ignore my pin numbers , I was looking at the PLCC MFP.

I figured it out for the 48 PIN MFP :)

Realized too that I don't have a pin out for the GST chip that has the integrated blitter, google returns zero results.

Found a service doc about shifting the chip when installing on a mega ste for an upgrade, but its not clear if that means numbers are different or there was an error on the board.

Have you looked here viewtopic.php?f=31&t=149

exxos wrote: 10 Dec 2022 01:02 Have you looked here viewtopic.php?f=31&t=149

Thank you, looks like the one marked in german is it!

So I removed the MFP, for those that don't have one, a cheap ebay hot air rework station works great as the last step! Especially for a large package like this with 48 pins.

I added fresh solder, and sucked as much as I could with a solder sucker, then using copper braid removed as much from the top of the chip as possible too.

The hot air station just lets me loosen the last bit. The only damage to the motherboard was some isolated trace material that was an island and disconnected from anything. Left over from etching, hard to see in the picture but its all superficial on the bottom, all traces intact!

Chip just needs to be cleaned if it still good, wish I had the rework station before I cut up my WDC Chip :(

For those curious, with no MFP you get a white screen on power. With test cart get a red screen in low res mode with garbage. Makes sense I think as mono is triggered via this chip.

If anyone is so inclined to read up on interrupts on the Atari ST, this is written by Dave Small, from Spectre and Magic Sac fame, Gadgets by Small.

https://www.atarimagazines.com/v5n2/Exc ... rupts.html

The MFP can generate 16 different interrupts. Furthermore, it will supply the 68000 with an address for those interrupts, skipping the whole auto-vector table above (even though it is a Level 6 interrupt). This is important because the 68000 doesn't have to spend time hunting around trying to find who interrupted it (polling). The MFP jumps the 68000 straight to the interrupt service routine.

Waiting on my socket to install and a replacement MFP too.

If this does not work, only thing I can think of next is clock or Midi Issues, for sure it was used for Midi as the ports have wear marks. The midi interrupts go through the MFP chip per the docs above.

Exxos, tell those postal workers to stop striking :)