[Coco] 6551 at 115200 bps (Roger's CoCo Net)

[Phill Harvey-Smith]

Steve wrote:
> To Roger and all...
[Snip!]
> On a side note: This need for quick timing loop is why Tandy used the 
> Halt and Load design for the Floppy Disk Controller.  The timing was too 
> tight to have the CPU test for a byte being ready so they just halted 
> the CPU till till the byte was there.  (It was up to the interrupt to 
> end the reading loop.)  Not the best design.  But it was cheap and worked.

It is doable, but it does require some 6809 tricks to do it, the Dragon 
Floppy controler did it by setting DP to $FF so that it could address 
the WD2797 with a 1 byte address as opposed to 2, e.g. LDA $40 instead 
of LDA $FF40 etc which saved a read cycle, and then used an FIRQ/SYNC 
loop to process the data, with NMI to break out of the loop when done.

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.