K-2 Kradle?

[1024MAK]

I timed how long it takes between power up and the K cursor appearing with a 16k RAM expansion, it was about 3 seconds for a UK spec ZX81. The standard BASIC ROM only looks for 16k of RAM (or less), so any extra RAM is ignored by the ROM, so will not affect the "start-up" time.

With BASIC, to use any RAM beyond the 16k bytes that it is expecting, you have to change a system variable (known as RAMTOP) with a POKE command. Then a NEW command. The instructions for the 64k byte Memotech RAM pack here explain more...

However, if you only want to store data above the normal RAMTOP limit, you can. No need to tell the BASIC system.

Note that the ROM does not perform a RAM test, it only tests to see how much RAM there is up to 16k bytes. All extra RAM is not tested or checked by the ROM.

Mark

[draketungsten]

@Moggy Thanks for the PDF and the tips. I saw a lot of demos that were cross-compiled on desktops and the speed possible with this thing is surprising. All I've read about Forth really is it's closer to machine than BASIC and so much faster, and at this time the only working chip on my board until I figure out why the Kradle apparently blocks boot.

@1024MAK Thanks for that, I wasn't aware it stops scanning at 16k. If I ever get the BASIC ROM to boot I'll give that POKE a try, not that I'd be doing anything with it but maybe in the future...

[David G]

Finally, there is a Kradle for sale on eBay: https://www.ebay.com/itm/335881401898 US $499 includes the Kradle and a Timex TS-1000 with vLA81 and new membrane keyboard and composite video mod

The Kradle looks to be in near-new condition. I like the way the keyboard hinges up, and then you put the ZX81 in and lower the keyboard back down.

Has some nice photos. It looks to be very nice build quality

More tactile keyboard with additional keys for common functions like List and Delete
64k of memory - 48k usable from Basic plus some lower memory for shadowing ROM or assembly routines
Joystick port that uses a standard Atari style joystick to essentially press the 4 arrow keys
Improved operation of cassette read/write
Pilot light

S/N K1065

The power supply doesn't seem to be right; it is only 650ma

[David G]

the listing has a lot of photos including

user manual

Hinged up

REV 1.0 board

Original box

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[David G]

the 1983 REV 1.0 board has
* eight HT 4264-20A RAM chips (64K x 1)
* Other chips look like 1982
* NEC ROM (?) is 1984? 8426 or B426
* large 1000uf capacitor
* TI LM393P 8-pin chip
* voltage regulator 78M05C

[1024MAK]

* TI LM393P 8-pin chip
* voltage regulator 78M05C

The LM393 is a comparator with an open collector output.

The 78M05 is a 500mA version of the 7805 5V voltage regulator.

I have to say, the unit does look impressive

Mark

[jdfan1000]

The seller scanned the manual for me: it’s on archive.com now. And listed on my page about the Kradle:
https://timexsinclair.com/product/kradle/

I have a Kradle and can take any addl photos you’d like.

David