Parallel Printer Interface (Centronics)
The parallel interface is also called Centronics interface.
It is mainly designed for printers with Centronics interface, but can also be used for
other peripheral devices with this interface.
Via the parallel interface 8 data bits can be transmitted simultaneously.
Additionally there are some control signals to handle a correct data transmission.
The interface contains 12 buffered ouput lines (8 data lines,
strobe, printer initialize, auto feed, select input) and 5
input lines (acknowlegde, busy, paper end, error, select), which are generated by the printer.
Block
diagram of the parallel interface
Signal level:
High = +5V, Low = 0V
Interface Pin Assignment
Top: IBM connector 25 pin D-SUB
female connector (socket) at the PC
Bottom: Centronics connector 36 pin
female connector (socket) at the printer
Minimum Connection between parallel PC Interface and Printer
D-SUB connector 25 pin <--------> Centronics connector 36 pin
| -STROBE |
1 |
------------ |
-STROBE |
1 |
| Data 0 |
2 |
------------ |
Data 0 |
2 |
| Data 1 |
3 |
------------ |
Data 1 |
3 |
| Data 2 |
4 |
------------ |
Data 2 |
4 |
| Data 3 |
5 |
------------ |
Data 3 |
5 |
| Data 4 |
6 |
------------ |
Data 4 |
6 |
| Data 5 |
7 |
------------ |
Data 5 |
7 |
| Data 6 |
8 |
------------ |
Data 6 |
8 |
| Data 7 |
9 |
------------ |
Data 7 |
9 |
| -ACK |
10 |
------------ |
-ACK |
10 |
| BUSY |
11 |
------------ |
BUSY |
11 |
| PE |
12 |
------------ |
PE |
12 |
| GND |
18 |
------------ |
GND |
30 |
Signal Description
Pin
Cen-
tronics |
Pin
D-SUB
25pin |
Signal
Source
> PC
< Device |
Signal
Name |
Function |
| 1 |
1 |
> |
-STROBE |
-Strobe = "0" data are transmitted to the printer |
| 2 |
2
|
<> |
Data
0 |
data line 0 |
| 3 |
3
|
<> |
Data
1 |
data line 1 |
| 4 |
4
|
<> |
Data
2 |
data line 2 |
| 5 |
5
|
<> |
Data
3 |
data line 3 |
| 6 |
6
|
<> |
Data
4 |
data line 4 |
| 7 |
7
|
<> |
Data
5 |
data line 5 |
| 8 |
8
|
<> |
Data
6 |
data line 6 |
| 9 |
9
|
<> |
Data
7 |
data line 7 |
| 10 |
10
|
< |
-ACK |
-ACK
= "0" the last character was accepted by the printer and a new one can be transmitted now |
| 11 |
11
|
< |
BUSY
|
BUSY
= "1" the printer is not able to receive new data |
| 12 |
12
|
< |
PE
|
PE =
"1" the printer ran out of paper |
| 13 |
13
|
< |
SLCT
|
SLCT
= "1" the printer is online |
| 14 |
14
|
> |
-AUTOFDX |
-AUTOFDX = "1" command to the printer to perform a line feed |
| 15 |
- |
|
- |
not used |
| 16 |
18
|
<> |
GND |
Signal ground |
| 17 |
- |
<> |
GND |
Chassis ground |
| 18 |
- |
< |
+5V |
+5V
from the printer |
| 19 |
- |
<> |
GND |
Ground twisted with -STROBE |
| 20 |
- |
<> |
GND |
Ground twisted with Data 0 |
| 21 |
- |
<> |
GND |
Ground twisted with Data 1 |
| 22 |
- |
<> |
GND |
Ground twisted with Data 2 |
| 23 |
- |
<> |
GND |
Ground twisted with Data 3 |
| 24 |
- |
<> |
GND |
Ground twisted with Data 4 |
| 25 |
- |
<> |
GND |
Ground twisted with Data 5 |
| 26 |
- |
<> |
GND |
Ground twisted with Data 6 |
| 27 |
- |
<> |
GND |
Ground twisted with Data 7 |
| 28 |
- |
<> |
GND |
Ground twisted with -ACK |
| 29 |
- |
<> |
GND |
Ground twisted with BUSY |
| 30 |
19
|
<> |
GND |
Ground |
| 31 |
16
|
> |
-INIT |
-INIT = "0" initializes the printer and clears the printer buffer |
| 32 |
15
|
< |
-ERROR |
-ERROR = "0" the printer is in error mode |
| 33 |
20
|
<> |
GND |
|
| 34 |
- |
|
- |
not used |
| 35 |
- |
< |
- |
Pull
Up to +5V |
| 36 |
17
|
> |
-SLCTlN |
-SLCTIN = "0" enables the printer to receive new data |
| - |
21,
22
23, 24
25 |
<> |
GND |
Ground |
Remark: The "minus" character (-) in front of a signal means that this
signal is "low active".
Output Timing of the parallel Interface
Timing of the signal lines at the output of data via the parllel interface.
25pin D-Sub
Loopback Connector
Using the following connector wireing a test adapter can be made to check the
function of a parallel interace at the PC.
1 to 13 (strobe to select)
2 to 15 (data0 to ERROR)
10 to 16 (ACK to INIT)
11 to 17 (BUSY to SLCTIN)
12 to 14 (PAPER END to AUTOFEED)
Parallel Interlink Cable (WIN95/WIN98)
With this cable a communication connection between two PCs can be set up
e.g. for WIN95, WIN98 or various transmission programs:
| DB-25(plug) |
|
DB-25(plug) |
| 2 |
<----> |
15 |
| 3 |
<----> |
13 |
| 4 |
<----> |
12 |
| 5 |
<----> |
10 |
| 6 |
<----> |
11 |
| 15 |
<----> |
2 |
| 13 |
<----> |
3 |
| 12 |
<----> |
4 |
| 10 |
<----> |
5 |
| 11 |
<----> |
6 |
| 25 |
<----> |
25 |
