WANTED SPECTRUM NTSC ULA

[gammaray]

Are there any available anywhere? Ben from ByteDelight says there are some...rare.

WILL A TIMEX SINCLAIR 2068 HAVE A PROPER ULA?

[RWAP]

There is one for sale on sellmyretro at the moment (although not cheap) :

https://www.sellmyretro.com/offer/detai ... -kit-11893

However, I understand that the SLAM48 will be out soon (a Spectrum 48K ULA replacement) which will also be listed on sellmyretro.com (other SLAMs are on there at the moment, but they are for 128K models). The SLAM48 will include a jumper for an NTSC mode.

[McKlaud]

WILL A TIMEX SINCLAIR 2068 HAVE A PROPER ULA?

What do you mean by that? TS2068 has its own ULA equivalent called TS2000. Generally this chip design was based on the Sinclair's ULA (one of 5C series), but it has different pinout and some additional functionality like Timex specific graphic modes and RGB signals. And yes, Timex SCLD is NTSC compatible.

If you are looking for the TS2000 replacement you need a lot of luck to find any spare in the wild.

[gammaray]

Well the issues would be:

Incompatibilities between Spectrum and TS2068. Would they extend to ULA? Or would it be identical as simply a NTSC version of Spectrum ULA?

I am sensing not...

[McKlaud]

All incompatibilities are results of using different ports for some peripherals like the AY-chip or Kempston interface, not the core design like ULA or memory access or interfaces between the CPU and the ULA. Bear in mind that there are major differences in the content of ROM and totally different arrangement of the edge connector. Signals on the edge connector were laid down in similar way to ZX81, not ZX Spectrum. However, if you disable both internal ROMs, use Sinclair ROM (precisely Timex Computer 2048 version one) instead and the "twister board" you will get a 99% compatible clone with ZX Spectrum 48K. I've also read somewhre on the net that someone substituted the Timex SCLD with a genuine ZX Spectrum ULA and it worked as it should. All additional graphic modes were lost and I am sure what modification were done to the video output circularity if any. It seems that the replacement is feasible.

[gammaray]

I am reading on SMR that a faster timing crystal is necessary. There are some NTSC chips for sale now on SMR but they are $$$$$$$$$$$$

[McKlaud]

TS2068 is NTSC machine as a default and 14.112Mhz & 3.579MHz crystals are in it. The kit on SMR is for an ordinary Speccy, which was designed to be used on this side of the pond, so with any PAL TV set. If you want to convert the PAL Speccy into NTSC one, yes, you need NTSC ULA and suitable crystals.

[1024MAK]

PAL and NTSC use slightly different oscillator frequencies for the colour carrier frequency. So yes, different crystals are needed.

Mark

[gammaray]

I see the color frequency AC signal is superimposed over the DC. That is where the design variation is.

[superfo]

I have a Harlequin 128 issue 2E that can switch between PAL and NTSC by jumper. Also it can switch between 48k and 128k timing.
If anyone want to try let me know.