Re: 1551 Repair - 28 pin 6523 Wanted

From: Jim Brain <>
Date: Sun, 09 Mar 2014 12:56:03 -0500
Message-ID: <>
On 3/9/2014 4:01 AM, smf wrote:
>> If set to input in the DDR they should read as '1'
> Only if there is a pull up resistor on the undefined bits, which there 
> may or may not be.
> However it's only if the undefined values are actually somewhat 
> reliable and are required by code that you have a major problem. The 
> rom code can be analysed pretty easily without access to real hardware 
> to see whether it's sensitive to the undefined inputs, if it's not 
> then it's just accuracy for it's own sake (*).
Pragmatically, it would be helpful if the bits could be ignored safely.  
Holding them in registers kicks the needed register count up to 48 from 
24, pushing one into more expensive options.

Setting them to a specific value is possible (0 or 1), of course, at no 
additional charge.


       Message was sent through the cbm-hackers mailing list
Received on 2014-03-09 18:00:07

Archive generated by hypermail 2.2.0.