9 Aug
2011
9 Aug
'11
11 a.m.
They did NOT make provision for multiple FDC, although
they also didn't
take steps to block it.
The buffer to drive the DMA requrst line on the IBM FDC card is a 3-state
drvice, whit the eneable software-controllaable. Thus you can disable it
and allow some other device (like a second FDC) to use that DMA channel.
When the PC firsrt came out, the FDC was justabotu the only thing that
needed a DMA cahnnel. So the 3-start bufer was fitted by IBM to allow you
to do somthing they'd not really considered (more DMA devices, inclduing
a second FDC).
-tony