Some said they have CDOS and Cromemco disks

Randy McLaughlin cctech at
Sat Apr 16 13:37:31 CDT 2005

From: "Dave Dunfield" <dave04a at>
Sent: Saturday, April 16, 2005 10:45 AM
> Hi Randy,
>>If you have 64K of RAM RDOS can be copied to RAM giving you access to the
>>full 64K allowing Larger CDOS's:  Using a random address such as 1000H:
>>ld hl,0C000H
>>ld de,2000H
>>ld bc,1000H
>>ld a,1
>>out (40H),a
>>ld hl,2000H
>>ld de,0C000H
>>ld bc,1000H
>>Just use the substitute memory command to enter the above code (hex) and 
>>a g 1000 (a return returns to RDOS).  You are now running RDOS out of RAM.
>>You can have one 32K CDOS and maybe a 64K CDOS to transfer.  BTW you never
>>have to use 8080 only opcodes since RDOS & CDOS only run on Z80's.  Also 
>>above code can go in any free space and is not address dependent.
> I thought about doing this - in fact, you can use the 'T' command to cause
> RDOS to copyitself to RAM ... but I would like to keep it running in 32k
> as this is more easily achieved configuration in many cases.
> I've put together a bit of documentation, and I have the transfer program
> as well as CDOS and Cromix images ready to put up, however I'm having a 
> bit
> of trouble with permissions on the server (which is remote to me)... I
> hope I can get it resolved this weekend and get the files up.
> Regards,
> Dave
> -- 
> dave04a (at)    Dave Dunfield
> dunfield (dot)  Firmware development services & tools:
> com             Collector of vintage computing equipment:

The 'T' command is not available in all versions of RDOS, RDOS v1 (used on 
4FDC's) didn't support it and I'm not sure when it was added.  The above 
routine should work on all Cromemco FDC's.  Cromemco's memory handling 
evolved as time went on.


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