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Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 6:19 am
by Paul
Hi Charlie,
Thanks for explaining.
Yes it was me and I wondered why shipping was that cheap from New Zealand ;)
So this was shere good luck for me.
As vdrive is a trademark for the usb2spi device and not any idea of one of us nobody was offended in any way. It makes it necessary for us to make the context of the usage of the word vdrive clear enough but this can't do any harm. We wouldn't want to miss your vdrive because it's so good and makes us feel at home at our little Sinclair machines a little more than other devices do because look and behavior is much closer than any other device for our machines do.
Kind regards Paul

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 6:51 am
by mrtinb
Hi and a warm welcome. Looks like a great product.

Since you, by magic, just create one ULA after the other, :) how about a ULA for the Lambda 8300? It’s a little different than the ZX81 and has the charset (ROM) build into the ULA. :)

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 8:55 am
by Lardo Boffin
Moggy wrote:
Wed Aug 14, 2019 11:02 pm
Lardo Boffin wrote:
Wed Aug 14, 2019 6:02 pm
Thanks Moggy. I had missed those as well!

I will have to order a ton of them shortly when a pallet of zeddies of unknown working status arrive shortly. :D

There should have been two pallets arriving but instead the seller sent me a calculator by mistake!
Sorry lardo couldn't resist. :lol:



If it's a Sinclair calculator it might be worth more than the zeddy!!
Sadly it was a £10 Casio. :(

Hopefully a pallet of zeddies will be arriving today. 8-)

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 9:01 am
by Lardo Boffin
Hello Charlie and welcome on board!

It looks like you sold about 6 of these since moggy pointed them out yesterday. :D Happy days.

I’m sure you will get a lot of feedback from the folks on here. Your ULA certainly looks the business.

I notice it supports 32K of RAM - how would that be fitted?

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 10:12 am
by Bloodnok
Thanks for the warm welcome.
Lardo Boffin wrote:
I notice it supports 32K of RAM - how would that be fitted?
A 62256 static ram (or equivalent) is just placed directly on the address/data bus. No additional components needed. Tynemouth Software have a good how-to guide http://blog.tynemouthsoftware.co.uk/201 ... rsion.html
32K_RAM.JPG
vLA81 32K Schematic
To get the 0-8K ram mapping A13 needs to be connected to PIN 35 of the ULA. If A13 is not connected to the ULA socket then the high (16K-48K) or low (8K-40K) mappings are still available. A13 would need to be disconnected if an original ULA is used as A13 would clash with the resonator circuit.

Here's one I prepared earlier:
vLA81_sw1.jpg
vLA81 32K addon
For more info the user manual gives all the possible memory maps etc. and a few more details.
vLA81_user_manual_v1.2.pdf
vLA81 User Manual
(594.28 KiB) Downloaded 12 times

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 12:24 pm
by Moggy
QUOTE.

"It looks like you sold about 6 of these since moggy pointed them out yesterday. :D Happy days."

I WANT 10% !!!!!!!!!! :lol:

Seriously, welcome aboard Bloodnok ( A Goons fan perhaps?) and really excellent work. :D

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 3:42 pm
by Lardo Boffin
Thanks for the RAM heads-up Charlie.

I’m looking at the video output section. Does this have a native composite video output like Andy’s? Just not sure of the terminology. :D

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 9:00 pm
by 1024MAK
I prefer my internal RAM upgrade detailed here :D

Hello Bloodnok, welcome :D

I must admit, I could not resist buying one of your vLA81 Sinclair ZX81 ULA replacements.

When it arrives (and I can find some time) I’ll try hooking it up to the Zeddy that I used in the article on the site I linked to above. I’ll have to reroute one SRAM address line to the vLA81 pin 35 and wire up the remaining SRAM address line to the CPU A14 address line.

Mark

Re: I missed the hot cakes...

Posted: Thu Aug 15, 2019 9:14 pm
by 1024MAK
Lardo Boffin wrote:
Thu Aug 15, 2019 3:42 pm
Thanks for the RAM heads-up Charlie.

I’m looking at the video output section. Does this have a native composite video output like Andy’s? Just not sure of the terminology. :D
Reading the documentation, it appears the answer is Yes, it can do this if SW1 is off.

Mark

Re: I missed the hot cakes...

Posted: Fri Aug 16, 2019 1:09 am
by Bloodnok
Lardo Boffin wrote:
Thu Aug 15, 2019 3:42 pm
Thanks for the RAM heads-up Charlie.

I’m looking at the video output section. Does this have a native composite video output like Andy’s? Just not sure of the terminology. :D
Yes - the video output is designed to drive a 75 ohm monitor input directly (or through a capacitor if desired). Here's the schematic (fairly standard stuff):
ZX81_VDAC.JPG
vLA81 Video output
ZX81_VDAC.JPG (9.42 KiB) Viewed 181 times
The various resistors are to provide the different levels for standard video or the high level sync required for the modulator (and some video mod boards). With the vLA81 there is no need for a video mod of any kind, although the switch settings can be configured to support most existing mods so no changes to the existing ZX81 setup should be needed (there are always going to be exceptions of course - please let me know and I'll look into it).