CZ1500/TS1500 Board and electrolytic miss marking

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1024MAK
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Re: CZ1500/TS1500 Board and electrolytic miss marking

Post by 1024MAK »

bola_dor wrote: Fri Jul 24, 2020 10:30 pm I don't konw what does it exactly means but returns 64 ...
I am absolutely sure its running at 50Hz as argentinian broadcast is and was PAL-N ...
64 means that bit 6 is set on the “ULAs” input port, which means that the “ULA” is reading the 50/60Hz pin as set for 50Hz. The same as a U.K. ZX81. Hence the code in the ROM is using 50Hz timing.

If bit 6 was clear (logic low) then it would indicate 60Hz and the code in the ROM would use 60Hz timing.

So this means that the ROM is very likely to be the same as the TS1000 and the later (bug fixed) ZX81 ROMs.

Mark
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bola_dor
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Re: CZ1500/TS1500 Board and electrolytic miss marking

Post by bola_dor »

1024MAK wrote: Sat Jul 25, 2020 4:00 am
64 means that bit 6 is set on the “ULAs” input port, which means that the “ULA” is reading the 50/60Hz pin as set for 50Hz. The same as a U.K. ZX81. Hence the code in the ROM is using 50Hz timing.

If bit 6 was clear (logic low) then it would indicate 60Hz and the code in the ROM would use 60Hz timing.

So this means that the ROM is very likely to be the same as the TS1000 and the later (bug fixed) ZX81 ROMs.

Mark
Thats good to know.
I've looked in the net some pictures of the US board with 4116 Ram and it looks like ULA's pin 21 is not connected, if you ever confirm that linking 21 to GND makes a 50Hz TS1500 I would appreciate if you report back (mine is 21 to 18 and GND) ..
(Now I am going to build your buffer coposite mod as RF is making lots of noise.. )
Ernesto
ZX80 USA, ZX81UK, ZX Spectrum, ZX Spectrum+, ZX Spectrum 128+ UK, ZX Spectrum +2/A, Sinclair QL, CZ1000, CZ1500, CZ2000, CZ1000Plus, CZ1500Plus, CZ Spectrum, CZ Spectrum Plus, TK83, TK85, TK90X, TK95. TS2068. And more to come :D
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