"Different" ZX81's

[1024MAK]

That heatsink looks like something I could have made using sheet metal and my tin snips...

[Moggy]

The ULA looks interesting insomuch that it bears the fancy little "diode" logo found on NTSC ULA's.

[Fwapp]

On speccies that normally means it's manufactured in the UK, rather than in the Philippines.

[Moggy]

On speccies that normally means it's manufactured in the UK, rather than in the Philippines.

Hmm could be, I suppose but I,m 99% sure it donates an NTSC ULA rather than a pal item which as far as I'm aware will work in a pal system.

Note the ULA pictured on this zx81 USA chip and the one for sale on sell my retro which are just two examples...

http://www.sellmyretro.com/offer/detail ... -kit-11893


Every NTSC ULA I've come across bears this mark so I would say the symbol denotes what it is rather than where it was made.

[Fwapp]

Is the symbol the Ferranti logo?

I've only seen a couple of ZX81 ULA's with the logo, this one being one of them. The original Z80 was in the same date range and the modulator was connected "UK" wise before the ZX8CCB was fitted.

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The Spectrum had a dedicated NTSC ULA, the 6C011E-3, did Sinclair make a NTSC ULA for the ZX81? Might try the one out of my US Zeddy in one of my UK ones. Perhaps Sinclair used the "prettier" ULA's over in the US, and we had to make do with the utilitarian ones

[Moggy]

Do you know Fwapp I'm beginning to doubt myself now!!!

For some strange reason Plessey is running around my brain and I'm sure they kicked out a few chips for Ferranti with the "nice" writing on them but then again I was sure about my last post.

Ah knackers to it ignore me I'm spouting bollocks as usual!

[PokeMon]

For the monochrome ZX81 there is no difference between PAL and NTSC. The only difference is the number of frames and top and bottom margin but this is made in software through setting AF' register with the corresponding value (55 for PAL or 31 for NTSC). That's why the US version is more slowly while having cpu time of 2*31*60 (frames)=3720 nmi's per second while the PAL has 2*55*50=5500 nmi's per second. These are approximate values only.

The reason for different ULA's for the spectrum is that the picture is generate by hardware, not software and so there is a need for different timers for PAL and NTSC.

[Fwapp]

Do you know Fwapp I'm beginning to doubt myself now!!!

For some strange reason Plessey is running around my brain and I'm sure they kicked out a few chips for Ferranti with the "nice" writing on them but then again I was sure about my last post.

Ah knackers to it ignore me I'm spouting bollocks as usual!

Aww - I was getting all excited there was a new ULA type I had to go hunting for!

I had a look at my US one and it's not the logo'd type - Might be case of Sinclair fitting what they had to hand.

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I know Plessey bought Ferranti's microelectronics business. I have a couple of the Plessey made Spectrum ULA's that they made in the late 80's. Perhaps they also sub-contracted ULA manufacture for Ferranti?

Karl - thanks for the explanation

[Moggy]

Like I said Fwapp ignore me.

What I am going to do though is trawl the world find that bloody logo and report back!!!

Thanks from me too Karl great info as always.

[1024MAK]

Yes, it's the logo they used at that time period.

Mark