20 Jul
2007
20 Jul
'07
8:37 p.m.
On 7/20/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
The OSC signal was the 14.3xxx MHz master clcok signal
in the PC and XT...
It was used, of course, by the CGA card as the master clock for the video
and colour cubcarrier timing. Some other cards used it, often divided
down, as a master clock.
Is there a list anywhere of what cards tended to use that signal? I
ask because I manufacture the GG2 Bus+ bus adapter for the Amiga, and,
because that signal is on the ISA bus, the designer of the card
slapped a $3 oscillator on it to provide it. I have a number of
unassembled cards and, honestly, would like to leave that signal off
if there's no expectation of folks needing it.
These days, the most common use for an ISA bus on an Amiga are either
for Ethernet (NE2000 or SMC 80x3) or serial (8250/16550). There are
other drivers, but nobody really cares about those anymore.
Certainly, nobody I am aware of is hanging a CGA card off of an Amiga,
but there's no reason why it wouldn't work from a technical standpoint
(and the holes are on the board for the oscillator anyway).
So... after the AT faded away and folks were running EGA and VGA on
386s and up, was the 14.3xxx MHz signal still relevant, or just an
artifact?
-ethan
21 Jul
21 Jul
4:51 p.m.
New subject: 14.3xxx MHz signal on the ISA bus (was Re: Help identifying a
On 7/20/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Not that I know of. But it was used on quite a few cards you'd not
expect, just as a master clock. I know, for example, my POST card
(displayes the POST errror codes) divides OSC down by 2^n (for a large n)
to get the display multiplexing signal...
The OSC signal was the 14.3xxx MHz master clcok
signal in the PC and XT...
It was used, of course, by the CGA card as the master clock for the video
and colour cubcarrier timing. Some other cards used it, often divided
down, as a master clock.
Is there a list anywhere of what cards tended to use that signal? I ask because I manufacture the GG2 Bus+ bus adapter for
the Amiga, and,
because that signal is on the ISA bus, the designer of the card
slapped a $3 oscillator on it to provide it. I have a number of
unassembled cards and, honestly, would like to leave that signal off
if there's no expectation of folks needing it.
You seem to have a choice. Save $3 and have to put up with people
complaining (and even worse not complaining, but telling their friends
that your design doesn;t work right) or do things properly and fit that
oscillator.
-tony
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ard＠p850ug1.demon.co.uk -
ethan.dicks＠gmail.com