Forcing T1000 to display PAL instead of NTSC.

[yerzmyey]

T1000. Sounds like Terminator's model.

Anywayz.

Despite people say PAL/NTSC is a colour code way, well - it isn't. Entirely.
For us, users of monochrome machines, the most important thing isn't any colour (yuck! ),
but screen's refreshing.

In our case PAL means 50hz screen and NTSC means 60Hz. Wchich means we _can_ use our machines on given TV-set, or we can't.

A friend of mine wrote that forcing Timex 1000 to display PAL screen - is rather simple.
It's enough - he said - to cut off resistor 0 ohm signed as "R30". And it supposedly turns ULA into 50Hz mode.
Et voila - we have PAL machine.

1) Is that true?
2) If so - can anybody make a photo of motherboard with the resistor pointed out? (Or on some photo taken from Internet).

Have a nice weekend.
Y

[gozzo]

As far as I know, that should work.. but no good for a TS1500 as it doesn't use the sinclair ULA..
I did have an idea for an external unit to fit on the expansion socket which would make either the TS1000 or TS1500 run at 50Hz, by 'patching' 2 ROM addresses , haven't yet got round to building one yet and am not 100% sure if it would work as those addresses are within the keyboard/display loop and may affect timing..if interested I could post a photo of the circuit on here....

[yerzmyey]

Yes, mod for T1500 would be nice too!

Meanwhile, seems like I found the piece in Timex 1000:
http://zx81.republika.pl/ZX81_SCHEME.jpg

"R30 - USA ONLY". Hm.

[Bill H]

It does work on the ts1000 and it increases the speed to boot. Someone out there has a copy of my old website, www.ts1000.us and in there, not in the forum but the regular pages, I had a detailed write up of the speed changes with a table. I believe that it ( modified to run at 50hz) was actually faster using the benchmark program I had than a stock zx81 was.

Bill H

P.s. I am still lurking here every day watching. If anyone wants a project for the zx/ts google apple game server ( or apple disk server) or go here http://asciiexpress.net/gameserver/ and make a similar one for the zx/ts with fast load. Here is a cool video of it in action. http://asciiexpress.net/gameserver/gameserverclient.mov

[gozzo]

This was an idea a had a while back for a 'patcher' to force a TS1000/TS1500 to run at 50Hz , note that I haven't yet tried it, so no guarantees...

[RetroTechie]

As for original question: true, it's really that simple. That resistor hangs on an ULA pin which has a (weaker) internal pull-up. With resistor missing (PAL / 50 Hz), the ULA pin goes to logic high (1), with resistor present (NTSC / 60 Hz) the ULA pin is pulled to logic low (0). The resistor (R30) is found halfway between ULA and cooling plate on ZX81 / TS1000 board.

That logic level is copied to bit 6 on a keyboard read (I/O port FEh), and used to set a system variable (if I'm not mistaken: MARGIN, at 16424 / 4028h) that determines the # of empty lines above & below active display area. Which also explains the speed difference between 50/60 Hz modes: in 50 Hz mode that # of empty screen lines is higher -> more time to execute user programs between screen updates.

As far as I know, that should work.. but no good for a TS1500 as it doesn't use the sinclair ULA..

I'm not familiar with that particular machine or the ULA it uses, but I doubt it wouldn't have a similar pin to enable a hardware default for 50/60 Hz setting. I guess you'd have to go over those ULA pins to exclude which pins it's NOT, and then you'd probably be left with one or 2 pins that are somehow hardwired to ground or +5V (but not supply pins). Sounds like a nice little 'project' for a happy owner of one of these machines...

[gozzo]

I have a copy of the TS1500 circuit - albeit a poor quality one - and none of the ULA pins are listed as 60Hz or 50Hz - and as far as I know it was only sold in the US, so it would only be for 60Hz anyway... this ULA is totally different to the Zx81/TS1000 one, it is a square/four sided surface mount thingy..with more pins as it also handles the 16K dynamic ram control.. I'm not 100% sure if the ROM is the same as if you hold '2' ( I think.?) down when switching it on, it changes the TV output frequency to a different channel ! There was also a 'semi-clone' of the TS1500 produced by Microdigital of Brazil called a TK85, I think this runs at 60Hz - haven't yet tried mine - , but this has an all-discrete-logic circuit and an extra 2k EPROM.....has some improvements - has space on the board to take a AY-3-8912 sound chip, port addresses compatible with the ZON-X81 unit!!

[yerzmyey]

Thanks a lot RetroTechie,
and thx to all guyz here.
I do appreciate Your help.



_______EDIT___________
Gozzo, do You mean the TK85 has the ZonX on-board implemented, or is there only a place for it, on the mother-board?





.

[gozzo]

As I understand it, the AY chip and its associated parts were an 'optional extra' - yes, there are blank holes on the board ready for the parts,but maybe some were ready-fitted with it? Mine doesn't have it. There was a website showing the details of how to fit it but it doesn't exist anymore.

[Andy Rea]

RE. the TS 1500 and 50Hz, there is a solder bridge near the ULA marked 50/60hz however on my machine it does nothing i can get it to run at 50Hz by using a patched rom.

Andy