IBM 5150 PC Technical Reference (6025005, August, 1981) (PDF)

Relations among the ON LINE switch, SLCT IN signal,
DC1/DC3 code and interface signals are shown in Table
12 below.
Table 12. DCl/DC3 And Data Entry
ON LINE
SWITCH
SLCTIN DC llDC 3 ERROR BUSY ACKNLG SLCT DATA ENTRY
OFF-LINE HIGHILOW DC llDC 3 LOW HIGH Not LOW Impossible
Generated
DC I HIGH LOWI Generated HIGH Possible
HIGH
(Normal entry)
HIGH
DC 3 HIGH LOWI Generated LOW Possible
HIGH
(See Note 1.)
ON-LINE LOW DC llDC 3 HIGH LOW/ Generated HIGH Possible
HIGH
(N ormal entry)
NOTES
1: In Table 12, it is assumed that as soon as the Printer receives data, it sends back the ACKNLG signal,
though this data is not stored in the print buffer_ In this status, the Printer is waiting for the DC I
code for normal entry_
2: The DC I/OC 3 code is valid under the condition that the DIP switch pin 1-8 is OFF, namely, the
level of SLCT IN at the pin No_ 36 of the interface connector is "HIGH"_ When SLCT IN is "LOW",
the DC I/DC 3 code is not valid.
(14) NUL (Null)
The NUL code is regarded as the termination for tabulation
setting sequence (described in detail later).
(15) BEL (Bell) ~
When the BEL code is input, the buzzer sounds for about 3
seconds.
(16) Escape (ESC) control
(a) Escape numerical control
Input ofan "ESC" code followed by an ASCII numeric
code permits each of the following functions to be
performed.
1) ESC 0 (Escape 0)
Receipt of an "ESC" followed by ASCII code
"0" causes the line spacing to be set at 1/8 inch.
Input of the ESC 2 code or INIT signal to the
interface connector or turning the power off and on
again causes the line spacing to return to 1/6 inch.
2) ESC 1 (Escape 1)
Receipt of an "ESC" followed by ASCII code
"1" causes the line spacing to be set at 7 /72 inch. ~
Input of the ESC 2 code or INIT signal to the
interface connector or turning the power off and on
again causes the line spacing to return to 1/6 inch.
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