Vdrive

[mrtinb]

The VDrive explained in the first post, and in detail on the german board linked to in the first post has this schematic.


http://forum.tlienhard.com/phpBB3/viewt ... t=25#p3425

The post on the german board also describes a RAM schematic. Is this necessary for a VDrive? Or can the driver be loaded in regular RAM?

[Paul]

There are vdrive drivers for any ram area available. At least on request So no special ram is needed.
The idea of the ram schematic is to have it battery powered so after switching off the vdrive driver is still present and you don't need to load it via ear.
kind regards Paul

[mrtinb]

I understand, that the 74HTC367 passes data from 14-to-13 and 12-to-11 when 15 is low.

But I don't understand why 2-to-3, 4-to-5 and 6-to-7 is connected through the chip, because 1 is always low, because it's connected to ground. Couldn't these be connected without the chip?

[1024MAK]

Vdrive2 - Interface for ZX81 (for USB - Stick)

Vdrive2 - Interface for ZX81 (for USB - Stick)mono.png (60.51 KiB) Viewed 4388 times

From the datasheet:

The ’HC367 and ’HCT367 silicon gate CMOS three-state buffers are general purpose high-speed non-inverting buffers. They have high drive current outputs which enable high speed operation even when driving large bus capacitances. These circuits possess the low power dissipation of CMOS circuitry, yet have speeds comparable to low power Schottky TTL circuits. Both circuits are capable of driving up to 15 low power Schottky inputs.

Maybe the high speed, high drive of a buffer is required?

Mark

[mrtinb]

To answer my own question:

I found this article on Internet, that explains it very well: Digital Buffer Tutorial

[mrtinb]

I've tried to change the schematic for use with the ICs I had in my storage. So the 74367 is exchanged for two 74245s. And the Vdrive-USB is exchanged for the Arduino (ethernet)/SD-shield.

So now I'll have to put it together, and see if it works.

[Andy Rea]

i'm no vdrive expert but.... the Vdrive unit has an ftdi chip that does the heavy lifting ( usb control / fat file system ect ) and presents to the user a simple serial interface.... so erm unless your going to implement a file system on the zeddy the Vdrive drivers aint gonna work witg direct connections to an sd card, also ( i am not familiar with the Ethernet / sd shield ) sd card require 3.3v not 5v

regards Andy

[mrtinb]

Ah...

I think the misunderstanding for me was this:

Code: Select all

ZX81  ---  Vdrive-HW  ---  SPI-protocol           ---  Vdrive  (original)
ZX81  ---  Vdrive-HW  ---  SPI-protocol           ---  SD-card  (my idea)

But in reality it is:

Code: Select all

ZX81  ---  Vdrive-HW  ---  SPI-vinculum-protocol  ---  Vdrive  (original)
ZX81  ---  Vdrive-HW  ---  SPI-SD-card-protocol   ---  SD-card  (my idea)

And that's why it won't work.

I assumed SPI was a application protocol, but it seems it's a hardware protocol.

[Andy Rea]

you could if your a wiz at Z80 or a glutten for punishment try coding up fat-fs by Chan http://elm-chan.org/fsw/ff/00index_e.html.....

or heres is a crazy idea fat-fa works great on arduino, create code on the arduino that emulates the Vdrive protacol but using SD card for storage instead of usb

Andy

[mrtinb]

you could if your a wiz at Z80 or a glutten for punishment try coding up fat-fs by Chan http://elm-chan.org/fsw/ff/00index_e.html.....

or heres is a crazy idea fat-fa works great on arduino, create code on the arduino that emulates the Vdrive protacol but using SD card for storage instead of usb

I had the idea briefly, but threw it away quickly