Date   : Wed, 17 Aug 2005 19:28:47 +0100
From   : Tom Seddon <tom@...>
Subject: Re: FDC status register test - please help

Greg Cook wrote:
> Could a couple of volunteers please test the values of the 1770 status
> register after a disc operation?  Insert a blank floppy disc and type:
> 
> *SAVE BLOB E000 +1AFF
> *CAT
> *HELP
> PRINT "X1=&"; ~?&FE84; " X2=&"; ~?&FE80
> *LOAD BLOB
> PRINT "Y1=&"; ~?&FE84; " Y2=&"; ~?&FE80
> 
> Then please reply quoting the four values plus the name of your Disc
> Filing System.
> 
> Some controllers, real and emulated, don't update the track and index
> flags when idle, and it's alleged other boards invert them! (BeebEm
> declares a board-specific property, TR00_ActiveHigh.)  If that's true,
> how come the drive head doesn't co *crunch* when driven from these
> boards?

Presumably because there's a NOT "thingy" somewhere between drive and 
status register, which inverts the relevant bit of the status register? 
As far as I'm aware, that register just reflects what the drive is 
indicating, so it could be anything, even bits swizzled, without a 
problem, because the drive never sees any of it.

Though obviously the software would have to know about that.

With opus challenger, I got status register as 0 after each operation. 
The drive control is write only, but I got back &FF in case that's of 
any interest :)

--Tom