I might have found the reason why the interface is still not working.

At the moment it is stuck at the point where it is reading signals as “disk change”, “high density detection”, and more.

It seems the problem is in the level of the 4 signals from a delay-circuit that drive the motor-on signals on ‘each’ drive (as if anyone is going to use more than one or two drives on one interface).

This is the circuit part:



The red wire indicates one of the four signals that might cause the problem.
Because it’s connected by a 39k Ohm resistor to the 5V, the maximum current is limited to about 1.2 mA.

This should be enough, because the 74LS244 datasheet sais it requires less than 1.0 mA:



At 7V power input it only requires about 1 mA, so at 5V power input less than 1 mA.

But anyhow, the corresponding output of the signal 74LS244 is undefined (about 3.8 volt), so it seems the input current is too low.

I’m going to test this any minute!

I found some nice early ‘showcase’ pictures in my archive, and some more info which might make you more curious and may bring you to buying one in the future ;)

Click for large picture:

Some detailled technical information about the progress of the MB04 development:

Calibrating the WD2797

One of the problems I encountered was that I needed an oscilloscope for the calibration of the WD2797 floppy disk controller.
Obviously I didn’t have one J
So I looked around at some second-hand internet sites and found a Tektronix for only 50 euro! Calibration was no problem with the scope.

Tektronix 912

ENB switch

A small fault in the MB02 schematics that I downloaded from the 8BC was that the ENB enable / disable switch was not implemented correctly in the schematics.
The way it was implemented it shorted the output of a flip-flop to the ground. I fixed that (I simple took over the schematics in the first place, so it was also wrong on the prototype).

Booting issues

I still have problems with booting the ROM. I’m not sure what the cause is at this moment, but the ROM does not always start when I power up the computer.

Parallel controller

I really dislike the 3 port parallel 8255 controller. It’s huge, and it’s only function at the monent is the Kempston joystick port.
I might get the 8255 out of the interface…

Risk of damaging the Spectrum with the prototype

Because this prototype interface is very large (see the pictures from yesterday), the chance that you hit the interface of your Spectrum while it’s on, and cause short-circuit or another fatal connection problem, is there.

So I’m thinking of splitting the interface in two parts:
1. Connecting directly to the Spectrum: adress- and data-buffers, the Z80DMA (which needs to control data- and adress-lines directly), and maybe the PC-keyboard and mouse interface if it’s not possible to put them behind the buffers.
2. The main MB04 components

I would then like the two parts being connected by a flexible cable.
And I hope the main ‘flexible connected’ MB04 interface will fit into a nice euro-format case (10x16 cm), because there are many nice casings available for that format.

MBHDD

If I’m not mistaking, my EPROM programmer (Willem Eprom Programmer) is able to program Gal chips also, so I hope that I have the MBHDD interface ready in a few weeks.

Casing for the prototype

Because I will join the Sinclair User Group at the HCC Days in Holland in three weeks, I would like to put all the hardware in a transparent PC case.
I just found a couple second hand from Sunbeam, and I’m emailing those sellers at the moment.

Don’t hasitate to send me any questions!

Hi All,

It was a bit quiet here for a while, but at the moment I’m testing and debugging the MB04 prototype!
Here are a few low-res picures of the prototype (my 5 megapixel camera broke down two weeks ago… sorry!):



I’m testing on a (grey) Spectrum +2 and a Spectrum +2B (for compatibility checks).
Of course not on my Spectrum 128K - that’s because I don’t trust the prototype yet ;)

The prototype booted up the ROM at the first attempt! But unfortunately it did not load the system floppy.
This is probably due to some functions in the circuitry that check the type of disk in the drive, but not all diskdrives support this type of check (they simply don’t have the signals for it).

I expect to have the prototype running at the HCC Days in november (in less than three weeks!).

The prototype has the following functions right now:
- WD2797 Floppy Controller with High Density support
- 3 channel parallel 8255 controller
- Real Time Clock
- 512 KB sram!
- Z80DMA controller
- 64 KB ROM (only 16K used at the moment)

I have a PC keyboard interface ready; just have to connect and test it, so I must be able to show that also.
And I want to have the MBHDD2 harddisk interface ready.

I’m hoping to integrate all the prototype hardware in a transparent case like this one:



It should be large enough ;)

So come visit the Sinclair User Group @ the HCC days 2006 in Utrecht!

I think I have to use 2 pcb's because there is also a PC keyboard interface and IDE interface integrated.
Found a real nice casing. More info coming...

Pcb's:



Schematic (90% finished):