Tatung Computer Forum

On my TC01 I have perfect output from the 80-Column Card but no colour signals from the VDP outputs. This hasn't worked since I obtain the machine.

I checked VDP input signals /CSR and /CSW from IC32 pins 6 and 8 respectively, they are stuck Hi but /RD and /WR are changing state. The above two outputs of IC32 are controlled by signal /VDP from IC26 14 pin which is also stuck Hi. IC26 is obviously functioning as expected for other outputs as those associated features are working.

Before I dismember the computer to replace IC26 (LSl38) is there a 'switch' anywhere that could stop the colour graphics from being produced?

Mike

Have you checked that the jumpers are set to RGB output and not the standard YUV?

https://re-enthused.com/information/tat ... art-cable/

Check the images here for the jumper settings

It might help?

Regards
Mike.

Thanks Mike but that is way upstream from the problem, /VDP isn't even changing state to enable the processor.
I have changed IC26 as this is the source of /VDP but to no effect.

I discovered that link block M003 in the 80 Column module dictates, at switch on, if the video defers to the unit or standard. I hadn't thought to look in module manuals as I had already tried with the module disconnected. in the position the link was in I would never see VGA out. With the link swapped over the 80 column output did indeed stop but I had also read that CTRL-P should change from normal to 80 col video out but it doesn't have any effect other than to cause some boot disc activity! The manual doesn't mention if there is a CTRL sequence to change the other way; from the default of 80 to standard colour out.

The MOS ROM is version 1.21 so higher than than 1.1 as required for the 80 column module; what changes were made with those versions?

I have checked the address and /MREQ/M1 signals into IC26 using my Picoscope 2205MSO and all are present with some changes present when a continuous stream of characters are sent. I do not know if they are in the right order to produce output /VDP. I have to investigate if it is possible to set up a pattern match in the Picoscope but as they not creating the required output I presume something is out there and I am suspecting it lies in the firmware.

Mike

Sounds like you have an uphill struggle there!

I seem to remember CTRL+N being the switch the other way.

I have it labelled on my Einstein, but its packed away so cannot check at the moment.

Do you get UHF output to an analogue TV (if you have one)?

Nothing from the RF end of things, as I say the VDP is not being enabled.

Thanks for the hint about CTRL N; I will give that a try to see what happens.

Next steps:
1. What MOS ROM version does everyone else with a TC02 80 column have in use?

2. I am wondering if there is an error in the MOS ROM EPROM; is there a binary file available for 1.21?
If so I will pull the 2764 EPROM and compare them.

3. Is there a MOS ROM source listing available for any versions higher than 1.1?

Mike S

I have MOS 1.2 in mine Einstein and it works well with my 80 col card.

Have you tried the diagnostic firmware?

I thought I might have had a ROM dump somewhere but I can't seem to find it, just the diag firmware.

http://tatungeinstein.hopto.org/8-bit/T ... ourcecode/

You might find what you are looking for at the above link, I have not indexed anything, just dumped what I have into a set of folders.

Mike, sorry I didn't come straight back; I didn't know you replied as, despite notifications for everything being turned on and subscribed to the topic I am not getting any notifications and they are not going into spam. Oops! I just noticed the need for a tick in the box below.

Many thanks for the link, lots of good material there but I found the binaries for 1.2 and 1.2.1 elsewhere.

I must rig something up to easily transfer files to the Einstein, probably 3.5 floppy and sort out a Gotek if I get everything working. Any preferred suppliers for the Gotek?

Mike