8 Jan
2013
8 Jan
'13
4:46 a.m.
On Monday (01/07/2013 at 08:22AM -0800), Dave wrote:
From: Chris Elmquist <chrise at pobox.com>
The ACIA was run in divide-by-1, external clock mode, with the clock
being derived from the data using the clock extractor on the floppy drive
(originally) and other circuits over time. But it was still async,
with a start bit and 1 or 2 stop bits per byte.
The 6850 does not have a synchronous mode like a USART such as AMI
S2350, which has a true synchronous mode (can sync to a start byte per
frame rather than a start bit per byte) and was also popular in floppy
controllers such as the Heathkit H-17 and Percom LFD-400 for SS-50 bus
both 10-hole hard-sector, and all from about the same time.
Chris
--
Chris Elmquist
I think you will find that the C1 used an async
UART (MC6850) and a PIA
(MC6820) to interface to the floppy drives.?
Actually, the ACIA was used in synchronous mode, and the MFM encoding was derived from
both the clock and data signals.