Thursday, 30 November 2017

Sinclair QL EPROM

A 28C128 EPROM chip can be connected to the Sinclair QL through the 16K plug-in cartridge ROM port. The memory occupies the space (0xC000-0xFFFF).

I can't guarantee this is the 100% definite way to do it, as I haven't been able to compare this to an existing EPROM cartridge. But it worked for me.

The diagram below shows the basic connections between the QL ROM port pins and the EPROM, with a 7400 chip between.

The 7400 IC should be connected to the 5V and GND too. In addition, two capacitors should be connected to 5V / GND near the two ICs. I had 100nF, which I hope to be ok.

In the above diagram, the NAND gates represent the activity of a 7400 IC for combining the signal of A14, A15 and ROMOEH, connecting the final output to the pin that controls the EPROM enable state. (Low=enable) The data lines should only be active when all of the A14, A15 and ROMOEH signals are high.

I was unsure about the role between -G (gate control) and -E (standby), as the device works when connecting both together. According to the EPROM datasheet the -G is used to set output enable/disable whereas the -E can be held low for device selection.

"Data is available at the outputs after the falling edge of G, assuming that E has been low [...]" makes me think that it's not a big deal timing-wise but it might be clearer if E was low all the time.

I have three QLs, and my first cartridge attempt worked in one of them. This led me to waste time thinking the "fault" could have been something about the differences in the QL models. In this version I had left the A14 and A15 floating, assuming the ROMOEH signal is enough to indicate the 16K area is addressed.

However as it should have been quite obvious from the start, the signals of A14 and A15 need to be combined with the ROMOEH, as the ROMOEH signal is high whenever the whole ROM area (0x0000-0xFFFF) is being read, not just the 16K area.

I used a Toolkit II ROM as a guinea pig. The onboard ROM (version JS) seems to find it "twice" which I hope is normal. The TK2 functions can be activated with the TK2_EXT command and all seemed to be ok.

An EPROM cart like this isn't especially useful these days, as many modern expansions do not work at the same time. Full 64K on-board ROM? Can't use the port. QL-SD? Can't use the port. Tetroid Disk Interface? Can't use the port. So, I'm left with a QL that can have a 16K EPROM and pretty much nothing else.

However this might be the beginnings for making something else, a transfer device etc.

Edit 14.12.2017: I burned 2.20 version of the Toolkit II, which has the FSERVE fileserver. The file server works nicely from the ROM module and is a quite powerful function to have. It alone justifies this little project, maybe I'll write about it later.

The parts list:

-27C128 EPROM + 28 pin socket
-7400 NAND chip, such as SN74LS00, + optional 14 pin socket
-2 x capacitor, I used 100nF

(Ignore the top image which has all kinds of unnecessary things added to it.)

The board

I have been hunting for a good PCB prototype board that would suit the project. It should be obviously with 2.54mm raster and double-sided so that it may have something that works as an edge connector.

I ordered a set from eBay with different sizes. The 50 x 70mm board with 18 x 24 raster is simply a perfect fit for the QL ROM cartridge slot, and there are 16  pads at the edges that just about work for the connector after modifying the board a bit.

The sixth position is cut off, to a depth that includes only the first through-hole. The QL case slot is wide enough for the 50mm width so nothing else needs to be cut.

The prototyping board and the blade for removing through-plating.
The raster holes are plated through, and as the pads are very short, this means the holes would immediately short the top and bottom connector pins. I suppose a variant without through-plating might exist, but it is difficult to tell from the eBay listings.

I rotated a paper/exacto knife blade from both sides of the hole, this way I could get rid of the through-plating from the row nearest to the pads. After all it is a very thin layering. This needs to be done briskly enough so that the chipping away can be felt, yet carefully enough so that the holes don't get ruined.

In the first row I need to be certain there is no contact between the two sides, no dust or thin filaments. This phase adds a bit of tedious handiwork.

The cut could be deeper but then the next row of through-plating should be removed too. One row is just enough for holding the cart in place. The pad width acted as a good guide for the cut width in this prototyping board.

What follows after is likewise tedious connecting of the pads to the chips by wire, for both sides. There shouldn't be too much solder on the pads, so I tinned the wires beforehand and tried to carefully connect them to the pad edges. Even then I made a bit of a mess, and I cut away extra solder with the paper knife.

There's a method for creating paths by solder for this type of board, but it's also slow and results in huge lumps of solder. I used wires for connecting nearly everything.

Friday, 3 November 2017

Sinclair QL Tetroid disk interface / memory expansion

The Tetroid Disk Interface is a memory expansion, disk interface and card reader for the Sinclair QL. It adds 768K memory to the 128 of the plain vanilla QL, totaling the memory to 896 kilobytes.

I ordered this from Russian Federation via eBay, with a Compact Flash (CF) card thrown in. The seller is identified as "tetroid" around forums and SellMyRetro site, so the interface is called Tetroid Disk Interface. The device can be considered an extended clone of a Miracle Trump card for the QL.

Fitting inside the case

Looking at the board, I check the jumpers are in good position for the plain QL, as instructed by the manual leaflet. Three jumpers turn on/off the disk interface, the QUBIDE/QUBATA interface and the extra memory.

Before I could get the card to fit, I had to whittle away just a tiny amount of the plastic from the QL with a paper knife. After this the card slides easy along the rails and fits comfortably to the extension port. The card sinks in completely, only the CF card protrudes slightly over the QL footprint: beautiful.

First boot up experience

Booting the QL with the included Compact Flash card, my first thought was: "It takes a bit long to get to the BASIC". But the CF card is filled with goodies and extensions that load on start-up, so the QL eventually ends up with a sort of graphical desktop.

Glancing at all the start-up messages, there are ToolKit 2, Q_Liberator (basic compiler?) , TURBO TOOLKIT (another basic compiler?), Pointer Toolkit, Qmenu, Scrap, History Device...  The CF card contents are a very thoughtful inclusion and makes me already feel I have something new to explore. (Edit: It seems I've maybe misunderstood this a bit, it's not that all the above software is on the card, but the related runtime libraries needed. Anyway, there's a bundle of things on the card)

As the QL has multi-tasking, a notepad, a calculator and a BASIC command line window can be open at the same time. The GUI is a very early effort, many windows often show functions and technical details that are text-based anyway. All this is very interesting, but not my focus now. Perhaps at a later time...

Now I can move to writing on QL...
Funny to see that there is less than 480Kb left after everything has been loaded. That's still three times more than the normal 128, which wasn't all usable anyway.

Without the CF Card

Next I took the CF card out and booted the QL again. (Don't insert/remove the CF card when the power is on).

Boot time to SuperBASIC is fast, but I guess checking the 800K memory adds a bit to the process. I shed a tiny tear for every second added to the boot time, because for me directness is a major charm of old computers.

Left: Showing memory in BASIC, Right: after running the TK2
The Tetroid manual leaflet obviously does not explain how to use your QL or the extensions. It doesn't even describe the Trump card functions, so the manual for that device is recommended reading.

The PRINT (PEEK_L(163872)/1024-128) command I found from a QL forum can prove the 896 K of memory is there. But to make things more simple, the Toolkit II can be summoned from the interface. TK2_EXT command gives the command set. Now I can PRINT FREE_MEM to show the remaining memory. JOBS shows the multitasking jobs, FSERVE starts the file server, ED runs the improved BASIC line editor.

The floppy drive, if it is connected, can be accessed from FLP1_ and the Compact Flash card is WIN1_. If the FLP1_ is present the QL will run the boot file from there.

With this amount of memory, a RAM disk starts to make sense. Multiple microdrive contents could easily be run from the memory. The default virtual drive is RAM1_ and again the Trump Card manual is your friend.

It's also possible to break out of the CF card boot basic file (SPACE+CTRL). This way I can have a peek at the WIN1_ drive from SuperBASIC without loading all the files into memory. The boot file can of course be altered to stop the commands from running next time.

Using HxC Floppy Emulator

The Compact Flash card does not show up on my Linux system, as the CF card is apparently in a format that can only be accessed with a Windows-only image editor and the QL itself. As far as I understand, there's no way to read/write files directly like you would with the mountable images inside a ZX Spectrum DivIDE CF cards. There's also probably no easy way to access the image file with Linux at the moment.

Well, I have my HxC Floppy Emulator. It took some steps to set up, though, so I'll put my notes here for future use.

The basis for the following is the document Using an SD Memory Card with the Sinclair QL, which contains information about the disk format parameters.

There are a bunch of Jumpers at the backside of the HxC. The organisation of these may vary from model to model, I have a boxed one with the pins bending backward. To make the HxC work with my QL, the jumper needed to be at the top left corner:

To get the HxC Floppy emulator windowed utility working on Linux, I followed these instructions exactly:

(I have Linux Mint 18 Sarah 64-bit). The command line version does not seem to be sufficiently detailed to generate these kind of images.

After running the HxC Floppy Emulator, I followed the how-to document mentioned above.

Use settings to tick out "auto", and choose Generic Shugart, which probably is the default anyway.

At the HxC main panel, use Load RAW Image to get to the screen below. Configure the format according to the specifications from the "Using an SD card..." document, or follow this image at your peril.

I ignored all the parameters that could not be followed from the document.

I tried to generate an empty image with "Create Empty Floppy", but although the HxC accepted the image, the QL did not recognize it. (Edit: It might have needed formatting)

I then used Load RAW File to load an existing DD raw image that is based on an emulator file. This I did not create myself, but downloaded from a QL forum. It may or may not be available.

After OK'ing the result, it can then be exported from the HxC main menu as a .hfe file. Copy this to the SD card.

On the QL end, the HxC device is connected to the Tetroid. Turn on power for the HxC device. Select the hfe image. Turn on Sinclair QL. The drive is recognized as FLP1_ in SuperBASIC.

Here I have powered the HxC from the 5V / GND pins of an Arduino, which has no other purpose here. When powered with an 9V adapter, the 5V output should have enough amperes to run the HxC. Powered from an USB, maybe not so much. Anyway this may not be ideal and I'll move to a PC power unit when feasible.


I once looked at an SD card reader device called QL-SD. This was a very cheap alternative, a replacement for a microdrive, including the Minerva ROM upgrade in the deal. However it also took out some memory away so for a 128K machine it was also a bit of a downgrade. Moving files from and to the SD was also not straightforward as the files were inside a disk image, again not so easily accessible from Linux.

The Tetroid interface also adds RAM and the floppy interface, an all Trump card functions, something the QL-SD did not offer.

Do these devices work at the same time? I have not yet tested, but I think there's no reason why not.

26.11.2017: Addendum

I inserted the TDI to my QL-SD equipped Sinclair QL, which has the Minerva ROM (JSL1) that came with the QL-SD. The TDI works nicely, and depending on the three TDI jumper settings, I can get one or two of the drives on-line, but never all three of them.

Jumpers on:
J1: Memory : SDC1_ is available
J1+J2: Memory + Floppy : FLP1_ and SDC1_ are available.
J1+J3: Memory + CF : WIN1_ is available
J1+J2+J3: Memory + CF + Floppy : WIN1_ and FLP1_ are available.

At least all drives can be reachable in some ways. With configuration J1+J2 I could move files between HxC and the QL-SD, and with J1+J2+J3 between the CF and the HxC.