CF cards on classic machines (was Re: Another disk imaging project)

Jim Brain brain at
Fri Aug 5 09:08:47 CDT 2005

Paul Koning wrote:

>No... the classic PIO mode IDE registers are 8 bits wide, not 16.
>Some devices may allow 16 bit access as an optimization, but 8 bit
>accesses is all you need.  
The IDE command registers are all 8-bits wide, but the Data register is 
16 bits wide. You have to support a 16 bit transfer in order to get the 
data from the sector buffer (256 16 bit transfers nets you 512 bytes of 
data, the IDE std sector).  IN the newer 48 bit addressing mode, the LBA 
registers grow from 8 bits to 16 bits as well.

All the IDE code I've looked at does it this way.  I believe I have the 
ATA r4 spec here that states that as well. 

But, if you've noted a way to switch IDE into 8-bit mode, let me know.


Jim Brain, Brain Innovations
brain at                      
Dabbling in WWW, Embedded Systems, Old CBM computers, and Good Times!

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