Which A500 ROM Switcher Is This?

[Coolit]

I'm trying to find out some information about a ROM switcher that I acquired some time ago for my 500, I've decided to go ahead and fit it but I need to know some info about it first.

I don’t have a digital camera so cant post a picture but I'm hopping that a clear description will be just as good (I hope).

Firstly, this has been made by Power Computing, this I know as it’s etched onto the top surface of the circuit board under where one of the two ROM chips sit. The circuit board is 80mm x 50mm, bluey green in appearance and has a 10mm x 20mm square cut out of the top right corner.

Looking from above, with the rom text facing you there is a large capacitor to the right with 3 large resistors and a small resistor in the same area. On the left side there are three jumpers and one resistor, the top two jumpers are marked R L and D A.

The underside of the board has two rows of pins for connection to the motherboard rom slots, to the right of this, etched on the circuit board is PC517 and under this ISS A.

I remember when I purchased this I was told that a combination of keys switches between roms.

What I’m looking for is information firstly about the jumpers; I presume that they are to set which rom is default and the motherboard revision. I’d also like to know what the combination of keys are used to switch roms.

Thanks for any replies I get and sorry again that I don’t have a picture to show you.

P.S. Had a look on the big book of amiga hardware and its not listed :(

[leofoe]

Never seen a ROM-switcher that is managed from software. You always need to reboot when switching ROM's. That's why these boards always have a real switch attached to it. If it's missing, the board will have solder-points to attach one.

[Tahoe]

There are lots of ROM switcher that do NOT require a switch, my DKB MultiStart II is also a key combination switcher, hold CTRL-RA-LA for more then 4 seconds and it switches ROM's.

[Coolit]

Thanks for your reply.

The switcher doesn't have a switch or anywhere to add a switch to. I think you just reboot holding down the set keys and it switches ROM. If you just reboot and don't hold down any keys it boots with the default ROM, at least I think this is how it works, with luck someone will be able to clarify this, what the jumpers do and there settings.

I'm guessing being a Power Computer design quite a few people will have seen one of these before.

[Doobrey]

Coolit wrote:
The switcher doesn't have a switch or anywhere to add a switch to. I think you just reboot holding down the set keys and it switches ROM.

Maybe one of the jumpers is where they should attach to?

I haven't seen the PowerComputing switcher, but all the switchers I've seen that don't use a switch need 2 wires hooked up.
One attaches to one of the CIAs and snoops on the mouse buttons, or attaches to the keyboard controller to snoop on a certain keypress which depends what pin on the controller it's attached to.
The other taps into the reset signal from wherever's nearest/easiest.

AFAIK, there isn't any other way to detect keys/mouse unless the switcher has a microcontroller or maybe overlays a small rom at reset, but both of those ideas seem way OTT compared to clipping on 2 wires.

[Coolit]

You may be right Doobrey, I'm really not sure. I did have another good look over it and there are two small (1x16pin, 1x20pin) IC's under the ROM chips, I was thinking this is the logic that performs the switch :-?

[Doobrey]

Yup, probably just a simple latch circuit that takes it's input at reset and selects the ROM to use.
Any numbers on them ( 74xx74 or a 74xx02 ??)

[Coolit]

Yeah,

16 pin = P9230 also DM74LS123N the makers mark seems to be "AX"

20 pin = B9218 also GAL16V8-25LNC the makers mark seems to be "BR"

Also one of the chips has a small sticker with "tested 92" on it so im guessing that this product was made in 1992.

[Coolit]

I've just sent an email to Power Computing, with a little luck they will be able to help, I'll post any info they can give me as it may be needed by someone in the future.