Bell, And Null Decodes - Raytheon DIDS-400 Series Technical Manual

DIDS -402 -2AM13
When an ESC control code is shifted into D3, ESC decode A12. 8 is enabled
during 4(CTS+l). The leading edge of this pulse siznultaneously resets SDL and
BB 3, while the trailing edge toggle s the ESC flip-flop to a set condition.
Resetting SDL prohibits shifting the ESC code into zneznory, while the reset con-
dition of BB3 enables SG23 to shift the next character of the znessage into D3.
Once the ESC flip-flop is set, it reznains set until SDL goe s high to enable
3(CTS+1) to be gated through A2S. 3.
SDL in this instance will not go high until the cursor is located. When
the cursor appears in the character entry register, SDL goes high during
4(CTS+l) to enable seven fast clock pulses [3{CTS+1) through 3(CTS)] to shift
the control code into zneznory. Following this transfer, 3CTS+! occurs to reset
the ESC flip-flop through NAND-gate A2S. 3. This then returns the circuit to its
quiescent state.
When a control code is received without being preceded by ESC, all control
code decodes are enabled due to a high at the output of AIS. 6. The following text
de scribe s what occurs when each of the listed codes are received in this znanner.
4-22.4.4.1 CAN, DC3, DCI, CR, FE',. VT, RT, BS Decodes (see
figure 4-.35)
When any of these control codes are received without being preceded in the
znessage by ESC, the, applicable decode is enabled because of a high present
at AIS. 6. The decode output is used to accoznplish the specified edit or cursor
control operation; it siznultaneously appears at an input of either All. 8, AII.6 or
All. 12. This places a high going level at the clock input of Al7. 13 which
siznultaneously sets the CCC flip-flop and clears BB3. The coznbined effect of
these two operations is to allow the next character of the znessage to be shifted
into D3 by SG23 and to inhibit SDL until the edit or cursor control function is
coznpleted. Thus, the control code previously held in D3 is destroyed and
replaced by the next character of the znessage.
As soon as the edit or cursor control function is coznpleted, a Function
Coznplete level jazns the CCC flip-flop reset to once again enable AlS. 6. This,
in turn, results in enabling SDL as soon as the cursor is located and the charac-
ter held in D3 is shifted into the delay-line zneznory.
4-22.4.4.2 ENQ, BELL" and NULL Decodes
When any of these control codes are received, the SDL flip-flop and a
special one-character delay flip-flop are jaznzned set during 3CTS. The cozn-
bined effect of these two operations is to siznultaneously enable SDL and disable
D3 GATE, thereby enabling clock pulses to ·shift the next character frozn D2.
Since D3 GATE is disabled, the NULL, ENQ or BELL control code is
destroyed by shifting the character into the blank wall forzned by D3 GATE.
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