On 6/20/06, Paul Fulghum <[email protected]>
The old 16550 OUT2 output (MCR:3) used to be a truly
independant control output that was commonly used
with an external gate to connect/disconnect the
interrupt request to the ISA bus.
Reading the TL16C752B datasheet, it seems pretty clear
that this gating is performed internal to the device.
MCR:3 is no longer an independant, general purpose I/O.
The result is the same though: If you dink around with
MCR:3 you could disable interrupts in either case.
So I don't see this as more or less of a problem than
other 16550 type devices.
I didn't know of this historic use of the OUT2 pin to disable
interrupts. I'll put OUT2 on my list of things not to muck with. Is
there any similar historic use of OUT1?
Cheers,
Shaun
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