6 Jun
2005
6 Jun
'05
4:57 p.m.
On 6/6/05, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
The original IBM CGA card (and many clones of it) used
the 14.3... MHz
clock from the motherboard. This was divided by 4 on the CGA card to give
the NTSC colour subcarrier anr by 3 on the motherboard to give the
processor clock.
On the AT motherboard (both the 6 and 8 MHz versions) there's a separate
14.3... MHx oscillator to provide this clock signal...
Because it's part of the ISA definition, the GG2 Bus+ has a 14.3.. MHz
oscillator just to provide that one signal... it's the second most
expensive single part on the board (behind the 22V10 GAL). If I ever
do another build, I may just make it an option, since I've never seen
an I/O board that uses it either, certainly not the IDE, Ethernet, or
parallel/serial boards that are the options supported under AmigaDOS.
-ethan