27C400/800/160/320 emulator/ROM switcher

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cmorley
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27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Sun Aug 18, 2019 2:49 pm

I've been busy beavering away at my 27C400 EPROM emulator/ROM switcher.

There was a sneak peak in the "today I built" thread for those that saw. The prototype batch of boards are assembled and working now which is great.

It emulates EPROMs and is programmed by USB. ROM switching by way of active low input - e.g. connect to the reset line

27C400 - 256Kx16 or 512Kx8
27C800 - 512Kx16 or 1Mx8
27C160 - 1Mx16 or 2Mx8
27C320 - 2Mx16 or 4Mx8

With smaller ROM sizes you get more switch banks... so for the Master you get 8x 1Mbit (with half the FLASH chip wasted! :O )

It also supports the Commodore mask ROM pinout they used in rev 3 and rev 5 Amigas as well as JEDEC pinout.

I've got it working in Amigas now and just ordered some PCBs to use it in a Master :D Daniel has kindly offered to do some testing =D>

Boards:
Photo0736.jpg
With pins top:
Photo0732.jpg
With pins bottom:
Photo0733.jpg
Master MOS adapter:
Photo0731.jpg
Rev 5 Amiga 500 :O :
Photo0738.jpg

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danielj
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by danielj » Sun Aug 18, 2019 3:12 pm

:) :) =D>

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Fri Sep 06, 2019 7:22 am

Master MOS swticher adapter assembled. I will try it this weekend then if successful post one to a forum member for testing :D
Photo0796.jpg
edit: I just noticed the text on the 27C400 emulator is upside down compared to convention of notch on the left... added to the fix list
Last edited by cmorley on Fri Sep 06, 2019 7:23 am, edited 1 time in total.

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jgharston
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by jgharston » Fri Sep 06, 2019 8:44 am

cmorley wrote:
Sun Aug 18, 2019 2:49 pm
Master MOS adapter:Photo0731.jpg
Won't fit with a GoMMC as it overlaps the next socket. :(

Code: Select all

$ bbcbasic
PDP11 BBC BASIC IV Version 0.25
(C) Copyright J.G.Harston 1989,2005-2015
>_

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Elminster
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by Elminster » Fri Sep 06, 2019 8:51 am

With the Retroclinic switcher and the GoSDC in a Master I had to add another 2 or 3 turned pin sockets to get enough height to clear goSDC. Isn't pretty but works. Although now I have a BeebSCSI and several gotek I am thinking of retiring the gosdc from my primary master. Although there are a couple of nice features on gosdc.

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Fri Sep 06, 2019 8:56 am

I'm not fussed about GoSDC/MMC clash. A narrower (harder to assemble) adapter could be made - like my B modules which are only 0.05" wider than the socket. This is really a test of the EPROM emulator. It clears the jumpers and ECONET so that is good enough for me for now.

Works though. Control-BREAK to switch ROMs 8)
Photo0797.jpg
Photo0798.jpg
Edit: Configured in 8x 256KB ROM mode... I used MOS320 & MOS350 from JGH's mdfs.net for this test.
Last edited by cmorley on Fri Sep 06, 2019 8:57 am, edited 1 time in total.

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danielj
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by danielj » Fri Sep 06, 2019 9:04 am

Looking good. :)

d.

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Elminster
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by Elminster » Fri Sep 06, 2019 9:11 am

Just a random thought as I was trying to think of uses of the parallel port the other day. Rather than control-Break could you somehow hook into the parallel port to provide the signal for which MOS to select? I have given no thought to how that might work.

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by tom_seddon » Fri Sep 06, 2019 11:14 am

What's the programming procedure? Can it be reprogrammed in situ?

I'd be very interested in a straightforwardly re-programmable mega rom replacement!

--Tom

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Fri Sep 06, 2019 12:54 pm

tom_seddon wrote:
Fri Sep 06, 2019 11:14 am
What's the programming procedure? Can it be reprogrammed in situ?

I'd be very interested in a straightforwardly re-programmable mega rom replacement!
USB serial (virtual com port) programming. Yes in situ programming.

On the firmware todo list is to allow one of the GPIO outputs to be controlled by serial command. So makefile build, program & reset of target machine is possible 8)

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by myelin » Fri Sep 06, 2019 8:32 pm

Nice work... that is one densely routed board! My attempt at something similar a while back was about twice the width. I take it that that's a USB micro next to C10?
SW/EE from New Zealand, now in Mountain View, CA, making BBC/Electron hardware projects for fun.
Most interesting: Arcflash, FX2+PiTubeDirect Tube/Cartridge adapter, USB cart interface.

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Fri Sep 06, 2019 8:42 pm

4mil/4mil and 4 layer board with 3 signal and 1 ground & power.

Yes I have used an STM32F042 which doesn't require a crystal for the USB. Only 32KB of FLASH and 6KB of RAM though.

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danielj
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by danielj » Tue Sep 17, 2019 8:51 pm

So, this thing is bloody brilliant. 8 configurations on the Master, ctrl-break to switch. Remembers last setting. No knobs, switches or holes. :) Upload images over USB from a serial terminal with minimal fuss. What's not to love?

d.

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Elminster
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by Elminster » Tue Sep 17, 2019 10:00 pm

danielj wrote:
Tue Sep 17, 2019 8:51 pm
So, this thing is bloody brilliant. 8 configurations on the Master, ctrl-break to switch. Remembers last setting. No knobs, switches or holes. :) Upload images over USB from a serial terminal with minimal fuss. What's not to love?

d.
I tell you is what not to love. I replaced my retro clinic 2 Rom switcher, with the 4 Rom Scsi version 2 weeks ago. :( Curses

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by tom_seddon » Tue Sep 17, 2019 11:05 pm

I assume the flying lead means an ordinary switch or button would also be an option for switching configuration? I use CTRL+BREAK quite a lot when using the Beeb, and I'm not sure I want it doing an OS switch each time :)

--Tom

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by cmorley » Wed Sep 18, 2019 4:39 am

tom_seddon wrote:
Tue Sep 17, 2019 11:05 pm
I assume the flying lead means an ordinary switch or button would also be an option for switching configuration? I use CTRL+BREAK quite a lot when using the Beeb, and I'm not sure I want it doing an OS switch each time :)
There is a timer in firmware on the switch input currently set to 1.5s which is a looong BREAK press for a human. You do have other options. You could put a dedicated switch there, you could fit a rotary switch or toggle switches... or hook it to the printer port/user port. The device is generic.

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danielj
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Re: 27C400/800/160/320 emulator/ROM switcher

Post by danielj » Wed Sep 18, 2019 7:06 am

It's fine in practice. It really does require a long press to flip images, you won't do it by mistake. It can be set to remember the last used image on switch-on, which is very handy.

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Re: 27C400/800/160/320 emulator/ROM switcher

Post by tom_seddon » Wed Sep 18, 2019 10:41 am

Ah, excellent - that actually sounds like a very convenient arrangement!

Will definitely get one of these. It'll be great to finally be able to get rid of View and Viewsheet.

--Tom

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