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Interfacing
Parallel Interfacing
94
A method of transfering data from a computer to a printer through a parallel interface based on the
centronics standard.
Specifications:
• data transfer speed:
1000 cps minimum
• synchronization:
extemal STROBE pulse
• logic levels:
TIL (Transistor-Transistor-Logic) levels
• handshaking:
BUSY and ACK signals
• connector type:
57-30360 (AMPHENOL) or equivalent
• cable:
use a shielded cable (6'5"/1.95 meters) or less in length.
When the printer is processing data, the BUSY signal is high. The printer will not accept new data from
the computer. After the processing is completed, the BUSY signal goes low. (The BUSY signal is also
high when the printer is OFF LINE). When the BUSY signal occurs, the ACK signal goes low indicating
to the computer that the data has been processed and the printer is ready to accept more data. This
handshaking routine occurs each time a character is sent to the printer.
ON LINE
OFFLINE
PAPER OUT
Printer status signals
BUSY
SLCT
LOW
HIGH
HIGH
LOW
HIGH
LOW
~
8
V
000000000000000000
000000000000000000
36
19
Parallel interface connector (printer side)
Signal
Return
Direc-
pin
.
side
Signal
tlon
pin
Singal
pin
1
19
STB
13
2
20
DATA 1
14
3
21
DATA 2
15
4
22
DATA 3
16
5
23
DATA 4
Input
17
6
24
DATA 5
18
7
25
DATA 6
31
8
26
DATA 7
32
9
27
DATA 8
33
10
28
ACK
34
11
29
BUSY
Output
35
12
PO
36
Pin configuration (Parallel)
PO
ERROR
LOW
HIGH
LOW
LOW
HIGH
LOW
Return
Dlrec-
side
Signal
pin
tlon
SLCT
Output
AUTO FEEDXT
Input
SG
FG
+5V
Output
30
PRIME
Input
ERROR
Output
SG
;
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