6 Jan
2005
6 Jan
'05
6:09 a.m.
> "Binary reads from a device are not
> allowed" is the message at 8753 in DR-DOS 3.41.
On Wed, 5 Jan 2005, Vintage Computer Festival wrote:
The question I haven't seen answered yet is,
"Well, why the hell not???"
The real answer is: there is no out-of-band signalling, so one of
the 128 in-band symbols (SUB, 26 decimal) is chosen to mean "END
OF FILE". It's borrowed from CP/M-80; I don't know where DR got
it; it seems un-DEC-ish.
("Out of band" signalling is, for RS-232 et al, the hardware
handshake lines. No one likes them, everyone complains like
babies, so they have essentially been deprecated.)
The practical answer is: COMMAND.COM does something to the effect:
while ( byte available from the COM port)
read byte
is it Control-Z?
TERMINATE COPY COMMAND
is it Null?
--> bit bucket
is it Character MSDOS Doesn't Like?
--> bit bucket
...
copy byte to file
is DISK FULL?
TERMINATE COPY COMMAND
continue