by One of the motivating factors for building the first (OEM) 360
controller was a feature of the IBM controllor implementing hardwired
oscillators.
I originally added the ascii/tty software support to CP/67
(predecessor to VM/370) in such a way that the terminal handler would
dynamically determine which type of terminal was connected on a line
(regardless of dial-up or direct). The IBM controller did have a "SAD"
command which allowed dynamically associating a specific line-scanner
with a specific line. With appropriate sequence of commands, I found I
could dynamically distinguish whether the in-coming connection was a
"1050", "2740", "2741", or tty terminal.
I got it all working an put it into production (borrowing a ascii
translation table definition from an early IBM publication along with
some misc. "fixes", surprisingly I didn't pay any attention to the bit
reversal until later) ... only to have a IBM customer engineer inform
me that it wasn't suppose to work. The problem was that while it was
possible to use the "SAD" commands to dynamically instruct the IBM
controller which line-scanner to associate with which line ... the
oscillator (i.e. bit speed descrimination) was hard-wired. Since the
1050, 2740, and 2741 operated at 134 characters ... that was OK
... but the ttys (of the era) operated at 110 characters. It was
something of a fluke that it was possible to intermix dial-up 2741 and
dial-up tty coming in on the same line (i.e. a single "base" phone
number ... on a rotary sequence ... could be used for all types of
incoming terminal types) ... where the line-speed oscillator was
hard-wired.
One of the features of the OEM controller was to strobe in-coming
signal fast enuf to dynamically determine line speed (it wasn't until
this point that I realized that the IBM controller line-scanner was
also reversing the bit order). Unformatunately, there eventually was a
requirement that the OEM controller be "IBM" compatible ... and since
none of the standard IBM software supported dynamic terminal type
identification ... that feature atrophied.
My archives still have pastel blue 360/67 reference card (pub
#229-3174-0)
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Britton Lee | voice: 408-370-1400
PO Box 8 | fax: 408-370-1598
Los Gatos, Ca. 95031 |