Hi there,

Does anyone know which jumper (if any) I need to short to enable the ROM socket of a 1750 REU ?

I can see :

J5 - ROMHL
J4 - ROML
J3 - ROMH

None are shorted at the moment, and any ROM I put in the socket ends up with the C128 starting with a black screen.

Thanks!

Mark

I might be wrong but I thought the ROm socket only worked when the REU was connected to a C64 ?

The ROM socket definately works in 128 mode.  There is a jumper pad between the DMA controller and the ROM socket.  You need to close it with solder.

Hi

Do you have both 40 column and 80 column monitors connected?  If you only have one connected it may be that the ROM is forcing the C128 to start on the other monitor.

The 128 supports 3 different function ROM configurations in the REU ROM socket (It also has similar support for a ROM in the U36 socket on the C128 motherboard):

1. 16k ROM at $8000 thru $BFFF (ROML)
2. 16k ROM at $C000 thru $FFFF (ROMH)
3. 32k ROM at $8000 thru $FFFF (ROMHL)

A 32k ROM can also be made to appear as two separate 16k ROMs.

A 16k ROM would have a part number such as 27C128 and a 32k ROM would be 27C256.

So you need to determine the size of the ROM and configure the jumpers accordingly.  If you have a 32k ROM you short ROMHL; if you have a 16k ROM short ROML and try booting - if that doesn't work unshort ROML and short ROMH instead.

Note also that there are two types of REU controller chip: an oblong 64pin device and a square 68pin device.  You have the oblong one so you have the 3 jumpers.  REU's having the square one have only one ROM jumper (J2) which can be left as it is for 16k ROMs but the shorting track connecting two of the pads must be cut and then solder the unused pad to the middle pad to use a 32k ROM.

Hope that's of some use to you.

Cheers,
Paul

That's a superb looking answer, I shall give it a go over the weekend! :-)

Thanks

Mark

Any results to post?

I would like to give this a try as well!

I need to find a jumper block to go in the ROML ROMH ROMHL holes ... just not got around to doing it yet :-)