for sale: Commodore 1540 Hi-ROM chip: MOS 325303-01

[Overdoc]

Hello,

I am selling some very rare original MOS 325303-01 chips.
This is the Hi-ROM 1540 Floppy DOS chip, which makes the difference between a 1540 and a 1541 diskdrive.
Most 1540 drives have been converted to a 1541 by swapping this chip against a 901229 from a 1541.

I have not seen this chip for sale anywhere in the last few years, so this is the chance to restore a 1540 to it's original state

I am asking 20,- Euro per piece.
Also willing to trade for other chips or some interesting Commodore hardware.
If interested let me know. I have a handful left.

[WaveRider]

Hi, I am interested for two chips. Please send me a PM. Cheers

[Overdoc]

*bump*

Still have about a dozen of those for sale.

[WaveRider]

Money sent. Cheers

[dragos]

are these ceramic?

[Overdoc]

No, they are normal black chips, but original by MOS, no eprom substitutes

[dragos]

pics please

[Overdoc]

Opps, just noticed this post some month later....
Anyway, I still have some of those.
Here is a pic:
https://imgur.com/2K5AzDm

[llcameron]

Hello!

I would like to buy two of these! I have two 1540s both with EPROMs so I am assuming those are upgraded 1541 ROMs.

[llcameron]

I did finally manage to acquire a 1540.

My unit has a 325302-01 ROM, NOT the 325303-01 ROM. Are these different ROMs? Is my ROM an earlier firmware version? Doens't seem like it would be since the drive serial number is 106433 which seems like a fairly late version drive. But maybe that actually is unit 6433 which would be an early version.

ANyone have any additional information on 1540 ROM versioning?

[Mike]

My unit has a 325302-01 ROM,

This is the Lo-ROM chip ($C000..$DFFF), which is the same for the 1540 and early 1541 (the 1541-II got a new Lo-ROM).

NOT the 325303-01 ROM.

If you couldn't find that on the PCB, it most probably had been replaced by a 2764 EPROM(+adapter) carrying the 1541 Hi-ROM. The ftp URL below contains a ROM dump of the 1540 Hi-ROM, so you could retrofit it.

Anyone have any additional information on 1540 ROM versioning?

ftp://www.zimmers.net/pub/cbm/firmware/ ... index.html

There has been only one version of the 1540 CBM DOS.

[llcameron]

I've attached a photo of the circuit board. I have two other 1540s in various states of repair I purchased, but they all have the 2764 EPROM replacement.

So I think what you are saying is that the 325302-01 ROM was the original 1540 ROM, and it was replaced with the 325303-01 ROM image, burned onto a 2764 for replacing the 325302-01 ROM?

[Mike]

So I think what you are saying is that the 325302-01 ROM was the original 1540 ROM, [...]

No. What I said is, 325302-01 is the common Lo-ROM chip ($C000..$DFFF) for 1540 and early 1541 disk drives.

325303-01 is the 1540 Hi-ROM chip ($E000..$FFFF), and these two together contain the CBM DOS of the 1540.

The early 1541, as stated above, uses the same Lo-ROM, but a different Hi-ROM chip, with the chip IDs 901229-01, -02, -03 or -05. Instead of an EPROM, you got a 1541's 901229-02 as Hi-ROM into your 1540 drive. Simple as that, as stated in the OP:

Most 1540 drives have been converted to a 1541 by swapping [the 325303-01] against a 901229 from a 1541.

So, if you want your 1540 back to its original state (concerning the DOS), several options:

- ask Overdoc for a 325303-01 ROM,
- burn yourself a 2764 EPROM with the 325303-01 ROM contents and use an adapter socket,
- ask Eslapion, whether he still offers (ready-burned) Motorola MCM68764 EPROMs (they have 24 pins => direct drop-in replacement),
- ask MCes for a similar option with 27HC641 EPROMs (also 24 pins),
- or make an inquiry at vintage-computers.it for a MultiROM (I use one of these as BASIC ROM fix/replacement),
- ... take your pick.

Greetings,

Michael

[eslapion]

- ask Eslapion, whether he still offers (ready-burned) Motorola MCM68764 EPROMs (they have 24 pins => direct drop-in replacement),

I do!

[llcameron]

Mike - thanks for that clarification! I understand now just what exactly I have.

Eslapion - thanks for the offer for the EPROM. I think I'm going to hold out to get the original 325303-01 Hi-ROM though!