Re: Differences between 8501R1 and 8501R4

From: Gerrit Heitsch <*gerrit_at_laosinh.s.bawue.de*> Date: Thu, 5 Dec 2019 14:13:44 +0100 Message-ID: <d9d685dc-d42b-32a9-7796-352f4005f851_at_laosinh.s.bawue.de> · gerrit_at_laosinh.s.bawue.de

On 12/5/19 1:16 PM, Frank Wolf wrote:
> 
> 
> The 8501 still contains some left overs of the SYNC at the top where the 
> bias generator
> now resides. Therefore I guess that it came first or at the same time as 
> the 8500
> jsut has some wires removed or cut (compared to the 8501).

Not quite.. Bit 5 of the I/O-Port does not exist on the 8501 die while 
the 6510 and 8500 contain a full 8Bit port, you can set and read all 8 
Bits on them (*). So there must have been a few  more changes between 
8501 and 8500.

(*) Which suggests that the 6510T in the 1551 floppy is just a different 
bond out of the 6510 to get all 8 Bits accessible.

  Gerrit