The Sinclair QL Forum

Dave wrote:Well, what about the smallest QL backplane? Simply a 1->2 connector backplane that fits internal to the QL and lets you put your QubIDE card directly above another card? I made one of these for my own personal use. I then put an insulating layer under the top card and applied some vinyl to the metal keyboard backplate to prevent shorts. If I had it to do over I would just 3D print rails on either side that attach to the backplane to guide cards in nicely, plus a small 20mm card extender sleeve.

Hi Dave,

Can you post a picture of the back plane and extender sleeve.

I'll go one better. I am about to order four prototype boards so I'll order four of these too. I have enough PMs already that I know they will all be gone right away.

I got enough interest - five people contacted me about the mini backplane - that I popped into my favorite PCB designer and freshened up the design a little.

The card fits inside a QL and supports three positions. Two positions face left and one faces right, upside down over the CPU. I don't personally recommend that you use all three positions with old cards that suck juice and spit out heat. However it does make it perfectly reasonable to have a newly minted Trump Card and QubIDE with CF slot just above it facing left. Alternatively, you could have the Trump Card face left and the IDE card face right. As long as the total current draw of the cards is under 500mA everything is fine.

The card is TINY, 96.3mm x 20.6mm. I left as much room as possible around it to allow air to circulate in the QL case. It will come with two protective plastic shields so a top card can't short against a bottom card, or an inverted card can't short against the metal keyboard backplate.
I should get the PCBs and have everything assembled in around three weeks. then I'll work out my costs and sell them at cost price. I'll post photos and so on then. I will only be making 25 of these, and have parts on hand to make 8 until I order more male DIN41612 connectors.

If anyone has requests for a custom backplane, I can do something for you.

tofro wrote:

Silvester wrote:QLSD is nearly what you're looking for: It has an SPI port with at least 1 free select line you could use to chat with your AVRs.

I have ordered a programmer for the ispMach 4000 family of CPLDs. I have the source, and there is excellent room to make it into a general purpose SPI IC. I would be quite interested in doing a "just SPI" solution because it opens up some interesting areas like a completely new yet compatible graphics system.

Dave wrote:I have ordered a programmer for the ispMach 4000 family of CPLDs. I have the source, and there is excellent room to make it into a general purpose SPI IC. I would be quite interested in doing a "just SPI" solution because it opens up some interesting areas like a completely new yet compatible graphics system.

For graphics, where write access is performace critical, a ROM port solution is not very suitable. Write data must be coded into address lines, before a pseudo-read can "write" it.

Peter wrote:

Dave wrote:I have ordered a programmer for the ispMach 4000 family of CPLDs. I have the source, and there is excellent room to make it into a general purpose SPI IC. I would be quite interested in doing a "just SPI" solution because it opens up some interesting areas like a completely new yet compatible graphics system.

For graphics, where write access is performace critical, a ROM port solution is not very suitable. Write data must be coded into address lines, before a pseudo-read can "write" it.

I wasn't thinking of the ROM port.

I was thinking more along the lines of a controller detecting the video interrupt, then buffer disconnecting the (external) CPU from the QL and having it read out the SRAM copy of the screen to a video buffer by either parallel or SPI.

Write access to a register is not really performance critical. Read the register address to write a 0, + 1 to write a 1, and so on. Needs exactly the same time as reading. Because you need to reserve 256 addresses per r/w register, this method is not very usable to write to external memory.

Handling a limited number of I/O addresses like needed for SPI, though, is fine and fast.

Tobias

Hardware-wise no difference, but extra address register manipulation on software side for data write emulation.

tofro wrote:

Silvester wrote:
Could do with a prototyping PCB for ROM port, if enough are produced it could help with cheap DIY projects (soundchip, etc). Maybe with a fixed PAL to provide simple I/O facility to prototyping area (ie. using address lines for Write). So hopefully, if the worst happens, only the PAL is fried. Anyone had any experience with suitable PCBs (required thickness/reliable slot tracks) from suppliers (China?).

The simple ABS box (100x75x40mm), as used by Miracle for ROM port MIDI interface, has proved reliable. If slot for PCB is cut in right place it sits neatly and flat on back of QL (no ZX81 RAM pack wobble!). Would allow 90x70mm prototyping area. Could also neatly fit 16x2 LCD display (etc) in lid of box.

I've got a few ATmega328's (28 pin DIL) that would be interesting to interface to QL likewise. Hmm, reliable fast buffered SER?, USB/PS2 mouse/keyboard?. AFAIK sketches for USB/PS2 already exist.

QLSD is nearly what you're looking for: It has an SPI port with at least 1 free select line you could use to chat with your AVRs.

Tempting, but I already have enough mass storage devices for my QL's. The real problem is using it on my Gold card machine (or SGC+Aurora machine). AFAIK QLSD doesn't work with SGC/GC reliably, and it would also need to use the ROM port addresses for its Eprom driver.

Also the idea was to use the chips SPI port (& USART/SPI) external to QL.

I have largely tackled the incompatibility issue by impedance matching some lines and doing voltage level translation with a TXB0108.

It also picks up some induced noise in the cable from the controller to the socket board at 15.7 or 15.8KHz... Routing the cable away from the video area straight to the front of the QL then across to the front left side of the socket board cuts that noise by 6db or so. About 75%.