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DIDS-402-2AM13
b.
DA - The DA chCj.racter received from the CPU is identical to the
address transmitted during the enquiry portion of the enquiry:-
re$ponse sequence.
c.
TEXT - Text characte r s in this portion of the me s sage are written
onto the display terminal s.creen beginning at the cursor position.
d.
COMMAND - The command codes,
if
present. direct the Display
Te'rminal to perform either an edit or cursor control function.
Command codes have the following character designations: NUL.
STX, ETX, ENQ. BEL, BS, HT, LF, VT, FF, CR, DCl, DC3,
CAN, and ESC.
With the exception of LF, these codes are not stored
in the display terminal delay line unless they are preceded by the ESC
code.
The ASCII coding for these codes is shown in table 4-1 and a
summary of the functiqn performed by each code is provided in
table 4-2.
e.
ETX - Described in paragraph 4-11.
1~:
Table 4-2.
Action of ASCII Control Codes During Receive
ASCII Cdde
Meaning
Function Performed
~-----------4-------------------+-----------------------------------.----
NUL
Null
STX
Start-of-Text
ETX
End-of- Text
ENQ
Enquiry
Accomplish time-fill after certain
control codes have been received.
First character of any message
received from the C.PU.
Prepares
the Display Terminal to examine
the next data characte r for the
correct DA.
If
the correct DA is
received, the Display Terminal
: enters the receive mode.
If the
incorrect DA is received, the
message' is aborted.
4-13
Terminates the receive operation
unless preceded by an ESC code.
If preceded by an ESC code, the
ETX character is stored in the
delay line.
,
Initiate a transmission of data from'
the Display Terminal.
The ENQ
code is used to read the contents of
the display terminal delay line even
though the operator has not depressed
the END (one-step) or XMIT (two-
step) keys.
This is contrary to the
normal polling read directive in that
a directive to read under a no trans-
mit condition would normally elicit
a 'no business
I
response.
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