Write Data - Control Data 1700 Maintenance Manual

selection of the Write Mode.
WRITE DATA
Before data can transfer to the low speed teletypewriter Controller from the
computer, the TTY station must be placed into the Write Mode. Placing the TTY
Controller in Write Mode can be accomplished by a Select Write Mode Function.
SELECT WRITE MODE
A teletypewriter Select Write Mode function is indicated by bit 08 or the
function code being a logical 11111. This bit enters the TTY controller at
l3-C16-l2. If a Function Command (13-B19-28) and the Equipment 1, Station 1
signal (13-B19-6) are also present, AND gate
~
(Z13 module, page 13) will be
satisfied if the controller has a Busy status (l3-C16-9). Satisfaction of AND
gate
~Will
cause the Write Mode FF to set (placing the controller in Write
Mode) and generate a logical
"0"
at l3-C16-l4 which will cause a Reply to be
sent to the Common Synchronizer.
With the setting of the Write Mode FF,the AND gate feeding TP ~ becomes
enabled and Write Mode signals leave the module at pins 1, 6, and 4. The logical
"I" outputs of pins 1 and 6 enable the contents of the Holding Register (page 25)
to be sampled by the receiving unit (page printer and/or paper tape punch). The
logical
"I"
output of pin 4 enables the Data status bit at l7-C14-8. In Write
Mode, this status bit becomes a
"I"
whenever the Data Write FF sets. The condi-
tions for setting this FF
a~usy)
(Read
+
Write). The Busy condition already
exists (a prerequisite to setting Write Mode FF). The Read
+
Write condition
is not met, however, until the computer receives a Reply or Reject signal.
2-23
Rev. A