Search found 379 matches

by RetroTechie
Wed Apr 19, 2017 5:01 am
Forum: Sinclair Misc
Topic: Image on CRT's in Fast mode?
Replies: 12
Views: 3531

Image on CRT's in Fast mode?

Just a quick question: If you take an unmodified ZX81 (read: video output via VHF/UHF modulator), a good old CRT, and the ZX81 enters Fast mode, what is seen on the screen? I keep 'remembering' :? that in this case the CRT would output 'snow' (random pixels), same as between TV stations when searchi...
by RetroTechie
Fri Apr 14, 2017 12:42 am
Forum: Hardware
Topic: Problems with my ZX81s
Replies: 24
Views: 4400

Re: Problems with my ZX81s

For the edge connector, try using clean paper (no ink, fingerprints or 'glossy' layer etc). This acts as a very fine / very mild sandpaper. With no solvent of any kind. 8-) Regular printer paper works well. At first you'll see the paper catch black dirt, simply continue with another piece of clean p...
by RetroTechie
Wed Apr 12, 2017 7:19 pm
Forum: Hardware
Topic: Z80 CPU compatibility
Replies: 4
Views: 1412

Re: Z80 CPU compatibility

Just get a CMOS version (Z84 C 00xx), it'll run cooler. I've even had East-German Z80 clones (UB880 = 2.5 MHz version) working in a ZX81. Which isn't surprising since a 2.5 -> 3.25 MHz overclock is quite moderate by Z80 standards. 8-) Working fine in ZX81 but problems with peripherals attached = pro...
by RetroTechie
Mon Apr 10, 2017 5:43 pm
Forum: Hardware
Topic: ZX81 Chip Pin-outs
Replies: 22
Views: 12396

Re: ZX81 Chip Pin-outs

Just checked the above pdf. For some reason cbmbsw included the pinout of a 2K*8 PSEUDO -static RAM (a dynamic RAM with static RAM like pinout), which is USELESS . The only ZX81's that came from factory with 2K installed were TS1000's, and the RAM chips used there are standard pinout 2K*8 static (no...
by RetroTechie
Mon Apr 10, 2017 5:02 pm
Forum: Hardware
Topic: ZX81 Chip Pin-outs
Replies: 22
Views: 12396

Re: ZX81 Chip Pin-outs

Just go with the ZX81 schematic, and datasheet for the exact RAM IC's that are fitted. These are either 2 pieces 1K*4 bit RAMs, or a single 1K*8 bit RAM (or 2K*8 in the case of a US-sold TS1000, with LK1 wire link in LK2 position). All those RAM chips are static RAMs and have standard pinout. So unl...
by RetroTechie
Wed Mar 08, 2017 12:40 am
Forum: Hardware
Topic: ZX81 / Timex 1000 tape loading
Replies: 29
Views: 5956

Re: ZX81 / Timex 1000 tape loading

Filename is useful when there are multiple programs on a tape. Or a program consisting of several parts (somehow). But... nothing that couldn't be handled using a tape counter. If not using an MP3 player... :)

Outside that, LOAD "" works just as well.
by RetroTechie
Mon Mar 06, 2017 12:56 pm
Forum: SALES
Topic: "Pristine" ZX80 for sale on eBay
Replies: 20
Views: 6373

Re: "Pristine" ZX80 for sale on eBay

"Factory sealed"? Don't think I've ever seen original Sinclair boxing that included plastic wrapping as shown. Although I might be mistaken. I haven't seen that many original Sinclair unboxings... (let alone ZX80) :lol: But yeah more probably a previous owner wrapped it all up, and (at best) that p...
by RetroTechie
Thu Mar 02, 2017 11:24 pm
Forum: Hardware
Topic: Putting a ZX81 onto a CPLD
Replies: 59
Views: 11041

Re: Putting a ZX81 onto a CPLD

PLCC in general is well on the way of being phased out. When it's got more than a few pins, it's mostly QFP or BGA housings these days. Personally I like keeping a few PLCC parts around for development purposes. But that's about it. Wouldn't consider 'em for any type of series production. Not to men...
by RetroTechie
Thu Mar 02, 2017 6:51 pm
Forum: Hardware
Topic: Putting a ZX81 onto a CPLD
Replies: 59
Views: 11041

Re: Putting a ZX81 onto a CPLD

@sirmorris: Cypress MAX ePLD != Altera MAX. Different CPLD family, different manufacturers. Cypress doesn't seem to do CPLD's or FPGA's anymore these days... The way I see it: So much obsolete that original manufacturer doesn't even mention it anymore on their website. Software, datasheets, family o...
by RetroTechie
Mon Feb 20, 2017 10:54 am
Forum: Hardware
Topic: TS1000 ULA vs ZX81 ULA
Replies: 24
Views: 4800

Re: TS1000 ULA vs ZX81 ULA

ULA pin 22. Has an internal pull-up. Optionally pulled low by (external) resistor R30. Pin readable as bit 6 of I/O port FEh. The ZX81 ROM uses this bit to set system variable MARGIN (address 16424), which holds the number of blank lines in the top & bottom border. With the ULA pin low (R30 present)...