I missed the hot cakes...

[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

[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.

[Lardo Boffin]

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.

There should have been two pallets arriving but instead the seller sent me a calculator by mistake!

Sorry lardo couldn't resist.



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.

[Lardo Boffin]

Hello Charlie and welcome on board!

It looks like you sold about 6 of these since moggy pointed them out yesterday. 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?

[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

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 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 544 times

[Moggy]

QUOTE.

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

I WANT 10% !!!!!!!!!!

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

[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.

[1024MAK]

I prefer my internal RAM upgrade detailed here

Hello Bloodnok, welcome

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

[1024MAK]

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.

Reading the documentation, it appears the answer is Yes, it can do this if SW1 is off.

Mark

[Bloodnok]

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.

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):

vLA81 Video output

ZX81_VDAC.JPG (9.42 KiB) Viewed 8290 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).