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DIDS-402-2AMI3
in order to be satisfied.
If a connection is left open by not connecting certain
wiring, the as sociated gate input is enabled at all time s by a high at the open
input.
As shown in figure 4-24, when the RS and CS options are not employed,
flip-flop A 70.3 has the sole function of switching the R steering logic to an 'off'
condition.
In addition, the AND function of gates AS4. 12 and A70. 8 are effectively
eliminated from the transmit enable circuitry.
Other than eliminating the time
'delay between the request and clear-once-to-send, the elimination of the RS and
CS circuits has no effect on the operation of the transmit enable circuitry.
4-22.
1.
3.2 One-Step Transmit
When the one-step transmit option is employed, the transmit enable circuits
are activated by depressing only the END key.
When END is depressed, an ETX
code is inserted into delay-line memory and the cursor is automatically line or
frame reset.
A pulse, START XMIT, initiates the transmit operation in essen-
tially the same manner as depression of the XMIT key.
The option takes one of two forms depending upon still another option.
In
one form, the cursor is frame reset before transmission is initiated.
When this
form is employed, up to 1040 characters m.ay be transmitted depending upon the
location of the ETX code in memory.
In
the second form, the cursor is line reset
before transmission-and up. to 80 characters may be transmitted.
Again, the
number of transmitted characters depends upon where ETX was inserted on the
line.
Each form is described separately to assist in understanding the particular
type of option employ'ed at the user installation.
The first form of one-step transmit is accomplished by connecting a wire
between terminals D and E on the display logic board (see figure 4-25).
When
the END key is depressed, an ETX code is inserted into the character entry
register.
This ETX is decoded by NAND-gate A58. 8 and during 3CTS
a pulse
is developed at AI7.II.
This pulse jams the cursor reset flip-flop and'a cursor
reset function is initiated (see paragraph 4-23.3.5).
On
the next F..6. (one frame
time later), NAND-gate A39.
6
is enabled and START XMIT pulse is produced.
As shown in figure 4-24, this pulse initiates the transmit operation through
terminals BY -CA (polling) andBA-BC (enquiry-response).
In
the second form of one-step transmit, a wire is connected from terminal
D to
F
on the display logic board.
In this form, depressing the END key causes
the cursor to be line reset and transmission to be initiated from that point.
The
cursor is moved to the first character of the line position by sequentially initiating
the step-up and advance-line cursor control operations (see paragraphs 4-23.3. 9b
and 4-23.3.4, respectively).
The pulse pre sent at Al 7. 11 is coupled to the clock input of one - step flip-
flop A2S. 9 and to the jam-set input of step-up flip-flop A14.
6.
When A14.
6
goes
high, the step-up cursor control operation is initiated.
After the cursor has been
moved to the character position on the previous line corresponding to the position
of ETX on the original line, Step Up Complete resets the step-up flip-flop.
This
places a high at A14. 5 which enables one input to NAND-gate AI.
6.
The remaining
inputs are satisfied during 4CTS+l, and the output of AI.
6
is employed to jam
reset flip-flop A41.
6
which initiates the advance line function.
After the cursor
has been advanced to the first character position of the line containing the ETX
code, NAND-gate All. 11 is enabled to produce the START XMIT pulse.
4-60
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