Sinclair ZX80 / ZX81 / Z88 Forums

Hi all,
I recently saw a spate of Memotech keyboards going on ebay. While I watched the auctions with interest I decided not to get involved as this keyboard attaches to the zx81 port for the display buffer thingy (hmmm...that's a phrase I've used three times this week). Although the buffer the attachment allegedly has a through port my instincts were telling me it would not be compatible with the ZXpand but was unable to check this as I don't know how the buffer thing is wired.

So, I thought I would ask here if the keyboard with buffer is compatible, or if it can be 'easily' adapted by removing the buffer (I can't find any pics of the internal wiring of the memotech). If so I might consider opening the Jeff Federal Reserve Coffers and entering the fray if any of these come up again.

I've collected 2 dktronics spectrum keyboards (just can't find an 81 one) and may end up cannibalising one of these for the 81 - but I'd much rather not do that because... .

cheers
Jeff

The Memotech "buffer" that is used with a Memotech ZX81 keyboard only buffers the keyboard signals. The through port is a normal unbuffered through port.

The Spectrum dk'tronics keyboards may well work electrically with out modification, as I think the keyboard matrix is the same. Of course, the key tops labels are not...

Sorry, out of time - more later...

Mark

Hi Jeff.

Yes the Memotech works ok with the xpand no problems My main set-up consists of Memotech buffer with Memotech assembler and xpand behind.
There is no real need for the assembler come to think of it as I have its code as a p file and load/run it straight out of the xpand something I think is possible also with the Memocalc spread sheet module
I have most of the Memotech modules and the only one not to play ball with the xpand is the hi-res module which although initialises displays white speckles on black backgrounds in hi res mode.

I can recommend these keyboards had mine from new still going strong.
Only downside is the legends wear off quickly ( clear nail varnish solves that) plus this keyboard not suitable for Toddy Forth(I know of Your interest) as for some strange reason a normal single key press produces a string of said letter so very delicate touch type and much back spacing needed.

Moggy wrote:Yes the Memotech works ok with the xpand no problems <Snip>
Only downside is the legends wear off quickly ( clear nail varnish solves that) plus this keyboard not suitable for Toddy Forth(I know of Your interest) as for some strange reason a normal single key press produces a string of said letter so very delicate touch type and much back spacing needed.

It sounds like Toddy Forth does not have a very good key de-bounce software routine. This problem may affect other keyboards that have real key switches (and which will have at least some contact bounce where the contacts make/break a number of times before staying made while you finger is on the key, all in a few mS).

Mark

Hi Moggy and Mark!

Thanks both for the very useful info, I hope I get another opportunity to make use of it!

As I was reading your comments I confess to getting that gut-wrenching, sinking feeling (which I could go on to describe in much gorier detail) of having very stupidly missed a series of opportunities to get a keyboard.

I'm consoling myself with the drawbacks of the keys Moggy mentions. I discovered my own external keyboard (which I daren't remove from the zedi to which it is attached) is from Redditch Electronics. I found a letter from the the man who was RE who wrote suggesting I wait for a new keyboard he was developing putting the computer inside the box. But, at the time, I suppose the wait was too much for me.

But the Memotech sounds ideal as it can be easily moved between machines <thinks: a series of expletives..>

But thanks gentlemen, useful info, a lesson learned, and I return, fate-hardened, to ebay!
Jeff

Yes, as the Memotech plugs in the expansion port edge-connector, it can be easily moved between machines . Also dead handy for testing a Zeddy that has a broken membrane, or indeed for testing a Zeddy PCB that is uncased (during repairs) .

Anyway, next time, ask here first .

Mark

I instinctively reached for the 'like' button there Mark!

Yes, I will, the future is looking cannier already!
Jeff

1024MAK wrote:

Moggy wrote:Yes the Memotech works ok with the xpand no problems <Snip>
Only downside is the legends wear off quickly ( clear nail varnish solves that) plus this keyboard not suitable for Toddy Forth(I know of Your interest) as for some strange reason a normal single key press produces a string of said letter so very delicate touch type and much back spacing needed.

It sounds like Toddy Forth does not have a very good key de-bounce software routine. This problem may affect other keyboards that have real key switches (and which will have at least some contact bounce where the contacts make/break a number of times before staying made while you finger is on the key, all in a few mS).

Mark

Hi Mark.
Yes the same thing applies to My Kaydee keyboard as well and if I try hard enough in a small way on original keyboard. I sent Kelly a PM about this and yes He is aware of the de-bounce routine being a bit dodgy on real hardware, but as Toddy was originally written for emulator use He didn't envisage a problem with the real thing and now that he knows He is rewriting the de-bounce code.

He did say that altering the address that holds the repeat rate speed to a higher figure might help, but no all it does is slow the repeat rate down whilst the de-bounce remains the same.
The odd thing is that having taken a Memotech switch apart I noticed that the switch is a slide to make/break as opposed to pushing two contacts together as in traditional switches so I wondered does de-bounce affect these type of switches also?


Moggy.