Minerva MK2 with switchable JS?

[t0nyt]

I was wondering if it was feasible to “easily” adapt a Minerva MK2 remake board with a 128kb EPROM to hold and switch between both Minerva & JS please?

Obviously JS wouldn’t support the RTC/I2C

Any thoughts please?

Many thanks
Tony

[Pr0f]

I can't see any reason why that would not work in theory - with a switch to select the top address bit in the eprom / flash rom to switch between the 2 versions

[t0nyt]

I can't see any reason why that would not work in theory - with a switch to select the top address bit in the eprom / flash rom to switch between the 2 versions

Thanks Pr0f, that was what I was hoping may be possible

Not that I know what to connect to what with the switch though…

Many thanks
Tony

[Derek_Stewart]

Hi,

It has already been done by Tetroid and but available by alea:

https://github.com/alvaroalea/QL_ROM_Sw ... /tree/main

[t0nyt]

Hi,

It has already been done by Tetroid and but available by alea:

installed.jpg


https://github.com/alvaroalea/QL_ROM_Sw ... /tree/main

Hi Derek,

That's an 8 bank ROM switcher, I'm looking to turn a Minerva MK2 board into a 2 bank switcher for Minerva/JS so the RTC/I2C is available for the Minerva half of the ROM still, but have JS as my everyday ROM

Or do you mean there's info in there on switching a 128K EPROM between each 64KB bank please?

Many thanks
Tony

[martyn_hill]

Hi tonyt!

Adding a switchable 128kb EPROM is relatively straightforward - the most tedious part is accomodating the extra pins (A16 and Vcc) and re-routing the Vcc power pin from (current) pin28 to its new home. The Minerva carrier board already does the heavy-lifting of routing the A15 and CE signals to suit an EPROM.

The actual manual switching is pretty trivial - simply wire a SPDT (Single Pole, Double Throw) micro switch with 3-legs such that it's common leg (typically, it's middle pin) connects to the 128kb EPROM's A16 pin, and it's other two legs connect to 5v and Gnd respectively (which way round doesn't matter - just determines which bank of 64kb is addressed in which switch position.)

Good luck!

[Pr0f]

It's not a bad idea to wire a resistor - say 470 ohms between the switch common and ground too. That way the signal going to the eprom is either ground or 5v, but never floating.

[t0nyt]

Thanks, I've ordered some 128KB eeproms

I hadn't noticed the 128Kb has more pins...

Once I have the chips I'll re-read and try and work out what I need to do pin wise (I know nothing about this stuff really)

Many thanks
Tony

[Pr0f]

Luckily - although with an exception or two - the manufacturers of these memory chips did agree something of a standard.

If you put the 32 pin chip in the 28pin socket, so that chip is aligned such that the pins furthest away from the notch or spot on the chip are flush with the socket pin receptors - you will have 4 pins (2 on each side) hanging over.

On the left of the notch or dot, the top most pin (pin 1) is NC (Not Connected) and the next one pin2 - is A16 - so that's the line that needs the switch.

On the right hand side of the notch or dot - top most pin (pin32) is your VCC or 5V input, and the next one down (pin 31) is NC (Not connected).

The Pin 30 (which on the socket would be pin 28) is not connected on the 128K chip - which is handy - as it can be left with 5V attached to it.

[t0nyt]

Have just compared pinouts between the 64k & 128k chips and I think I understand

While I’m waiting for the 128k’s to arrive I’ll dig out a switch, wire and resistor ready

Will do a trial run on the socketed mk2 I built first and if all seems ok will try and build an un-socketed version that will fit inside a QL

Many thanks
Tony