On 30 Aug 2004 at 7:20, Jay West wrote:
Actually, it probably would have worked, as a common
(although not
required) setup for HP terminals was that the serial interface in the
host was set for external baud rate, and the terminal provided the
clocking.
Indeed, it did work. The 264x terminals had a rotary switch that set the
baud rate clock supplied to the interface from 9600 down to 110. It had a
final position, "EXT," to set the baud rate from a clock received from the
interface (though I don't recall ever seeing a terminal in use with this
position set). Some interfaces, such as the 12880A CRT interface, set
their communication rate from the clock supplied by the terminal.
With such a setup, one could slow down a terminal listing by rotating the
switch to a lower baud rate. Because the switch was a break-before-make
type, one could even "tease" the switch into an intermediate position
(e.g., between 9600 and 4800 baud) to freeze the listing.
But I don't know why anyone would. Two of the primary operating systems of
the day, DOS and RTE, had terminal interruptibility (and, although I'm not
certain, I seem to recall that TSB supported XON/XOFF). Pressing any key
while terminal output was in progress would pause the output between lines
and issue a prompt for a system command. So pausing a long listing was a
matter of hitting SPACE to stop and RETURN to resume.
The only times I ever recall using the baud rate switch to slow down the
output was when running the hardware diagnostics. Even then, a few
characters were typically lost during the switching, showing up as filled
boxes (the DEL character graphic) on the screen.
-- Dave