On Mon, 1 Feb 2010 , ard at p850ug1.demon.co.uk (Tony Duell) wrote:
That sounds more like the Intel 8251 USART. IIRC on that chip you have to
send the reset command 3 times to ensure it's treated as a command and
not as data to be loadrd into one of the configuration registers.
-tony
Hmm, I must be getting old.
Between about 1983 and about 1990, I wrote a fair amount of software for
a communications board which I designed, and which used an 8088, an
8259, an 8253, 8255s, and, for some reason I cannot remember now, I
think it used 6850s for the serial ports. We started out with all
Motorola peripheral chips but found out that the timer chip wouldn't
work properly together with the Intel bus, so we switched to Intel. I do
have the distinct impression that we kept the 6850s for some reason,
probably price, and, I think, simplicity. We had no need for synchronous
communications so that would have been a reason.
We had an earlier all-Motorola design (6809-based) we got ideas from (I
had never designed any microprocessor circuitry before), and IIRC, I
started out sending a single reset command, which didn't work, and then
I looked at the other design and saw that their software sent 3 resets,
which I then understood the reason for.
I may be wrong, as this was 27 years ago, but it would be easy to test. I
can't, as I have nothing to test on. And Charlie C, had you asked me 27
years ago I could have told you exactly what to do ;-)
Whatever it was I did, it worked well, because we sold a number of those
boards, each of which used 4 serial interfaces. It annoys me that I
can't be sure whether we kept the ACIAs or changed to Intel.
Wh?t I do remember is that the Motorola chips were simple and elegant
compared to the Intel chips.
/Jonas