It looks like the MOS 6500/1 is a second sourced Rockwell R6500/1. The R6500/1 was Rockwell's first 6502 based microcontroller, it's in their 1979 databook, and at that time was their only 6502 based microcontroller. It's big limitation is that it has no external bus, but there were emulator devices, one with a piggyback ROM socket and another in a 64 pin package that exposed enough address bus for a ROM and a little bit of extra RAM for debugging.

The MOS preliminary data sheet actually mentions that the MOS 6500/1 is compatible with the R6500/1E emulator.

Rockwells next microcontroller was the R6501Q, which did have an external bus, making it a lot more versatile, but it did come in a 64 pin package. I don't think they produced any other 40-pin microcontrollers so there isn't really much of an upgrade path from the 6500/1. The biggest issue with replacing it is that the stack is relocated to page 0, but it's not too hard to update the code.

So either a 6502 (or 6504 etc.) and a 6532 could probably be used, or a 6501Q with an external ROM. The R6501Q has 192 bytes of RAM, which should be more than enough. It's still relatively easy to find NOS 6501Q's, I have a box of 100 of them waiting for worthwhile projects.

An interesting possibility! Why would you think Rockwell are the original, and not themselves the second source?

Related recent dissection of the chip:
MOS 6571 Amiga keyboard controller dissection > 6500/1

I'm at home with RSV at present, so maybe not thinking straight. However I do have 3 ceramic R6500/1's in the workshop which I need to go out and check the date codes on.

I'm mainly going on the dates on the data sheets. Rockwell have 1979 dated data sheets as the earliest I could find (and 1987 as the latest). That's probably not conclusive as Commodore were particularly bad at updating datasheets, probably understandable as most of their production was for internal use.

The other clue is that one Commodore data sheet refers to the emulator as a R6500/1 emulator, this could mean that Commodore didn't produce any emulators (with their special packaging) and just used the Rockwell ones. In general the Rockwell data sheet is consistent with all their other data sheets, and the original Commodore one appears to be quite a close copy.

A counter argument could be that the die shot shows no Rockwell branding and a CSG logo?

NCR also produced them, looks like with Commodore ROM code in them, the one I found had an 83 date code.

But mainly I know about these as they are the start of a very long line of Rockwell 6502 microcontrollers, in the end only used in modems, which is unfortunate, the last standalone one, the L28 apparently runs at up to 35MHz. It has a 512k address range, with bank switching, and a multiply instruction.

Thanks! I might well guess that the Rockwell people working on 6502 cores - rather than variant chips - might have more expertise and more resources than CSG. This is evidently a new core, in the sense that there are quite deep changes to logic and layout.

Didn't know about the 6500/1. It reminds me of the 6805V1P which was a 6800 based microcontroler. Similarly speced.

To be fair, these are not hobbyist friendly parts so it seems reasonable they did not come to our attention back in the day. A company I worked for before I crossed over to the dark side (IT) used the 6805V1P to control a paper tape punch in a teleprinter. Remember those and the Telex service? Replaced by FAX which has now basically gone the way of the dodo too.

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Bill

I think they were the first 6502 based microcontrollers, but really at that time a 6502 with a 6532 was a good option, and a TIM monitor for development. For hobbyists it didn't really get useful until EPROM based microcontrollers became available, but really Rockwell did have some good development options. I've no idea how much they cost, they were probably expensive.

I found a couple of photos of the 6500/1's I have. The ceramic chip is a, rare for Rockwell, 64-pin ceramic chip that brings out extra pins for an EPROM for development. However this is not suitable for emulating in place. For that Rockwell had a piggyback package, shown in the other photo.