21 Jun
2006
21 Jun
'06
9:40 p.m.
Chuck Guzis wrote:
Reason? So the Peanut user could mess up his modem
and floppy transfers by
banging on the keyboard at the wrong time? Maybe to make sure that no one
would try to hack in an 8087 NDP?
I wonder if it was because the chicklet keybard had no internal buffering,
so NMI was thought to make it possible to grab keys as soon as they were
hit.
Cheers,
Chuck
The keyboard (chicklet or otherwise) does not buffer keystrokes, so the
8088 has to pull them as fast as they come. The non-maskable interrupt
is used to do the deserialization, which is what causes the mess with
the other I/O.
With the serial port sending data at 2400 bps the 8088 was fast enough
to service the keyboard without dropping characters. Above 2400 bps if
you used the keyboard you might lose something.
As for the diskette drive, I can't remember what the trick was, but the
machine had a way to disconnect the keyboard from the NMI while the
diskette was being serviced.