Centronix Parallel Ports

moved to Parallel Port Signal Detail

Fig 10-2
DB-25
Pin Driven by Signal Name Cent
Pin

1 Host /Strobe 1 Tells the printer that data is available on Data 0-7. Pulse width must be more than 0.5us. Must be high if Busy or /Acknowledge are also high. driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.

2 Host Data 0 2 Data lines must be valid 0.5us before falling edge of Strobe signal.
The Data Out pins were orginally driven by a 74LS374 octal latch, which could source 2.6 mA and sink 24 mA. It is essential that the external device not try to pull these lines to ground, as this might cause the 74LS374 to source more current than it could handle without damage. Exception: bidirectional printer ports allow the 74LS374 (or equivalent) driver chip to be tri-stated.

3 Host Data 1 3

4 Host Data 2 4

5 Host Data 3 5

6 Host Data 4 6

7 Host Data 5 7

8 Host Data 6 8

9 Host Data 7 9

10 Printer /Ack 10 Pulse width approx 3us. Asserted when Busy goes off or after data is accepted. Also pulsed when printer comes on line after power on, reset, or operater selects online mode. Inverted in Status Input register

11 Printer Busy 11 Indicates that the printer is busy. Asserted during reading of data, printing, errors, and when offline.

12 Printer Out of Paper 12

13 Printer Select 13 High when printer is online.

14 Host /Auto Feed 14 driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.

15 Printer /Error 32

16 Host /Initialize 31 driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors. Double inverted from the control register.

17 Host /Select Input 36 driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.

18-35 Both Ground 30

Ground returns 19-29

Fig 10-2
DB-25 Pin	Driven by	Signal Name	Cent Pin
1	Host	/Strobe	1	Tells the printer that data is available on Data 0-7. Pulse width must be more than 0.5us. Must be high if Busy or /Acknowledge are also high. driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.
2	Host	Data 0	2	Data lines must be valid 0.5us before falling edge of Strobe signal. The Data Out pins were orginally driven by a 74LS374 octal latch, which could source 2.6 mA and sink 24 mA. It is essential that the external device not try to pull these lines to ground, as this might cause the 74LS374 to source more current than it could handle without damage. Exception: bidirectional printer ports allow the 74LS374 (or equivalent) driver chip to be tri-stated.
3	Host	Data 1	3
4	Host	Data 2	4
5	Host	Data 3	5
6	Host	Data 4	6
7	Host	Data 5	7
8	Host	Data 6	8
9	Host	Data 7	9
10	Printer	/Ack	10	Pulse width approx 3us. Asserted when Busy goes off or after data is accepted. Also pulsed when printer comes on line after power on, reset, or operater selects online mode. Inverted in Status Input register
11	Printer	Busy	11	Indicates that the printer is busy. Asserted during reading of data, printing, errors, and when offline.
12	Printer	Out of Paper	12
13	Printer	Select	13	High when printer is online.
14	Host	/Auto Feed	14	driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.
15	Printer	/Error	32
16	Host	/Initialize	31	driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors. Double inverted from the control register.
17	Host	/Select Input	36	driven by 7405 inverting open collector buffers, pulled to +5 volts via 4.7K resistors.
18-35	Both	Ground	30
		Ground returns	19-29

IBM Parallel Port FAQ by Zhahai Stewart 1994
- "... writes various patterns to the data lines without every pulsing the -strobe line. Without a pulse on -strobe, any printer also attached to the port should ignore this data..."
Interfacing the Standard Parallel Port
Section10 IBM PC Inside/Out
Null port connector
State Machine for the Parallel Port output
The elab inc. 1 chip (PIC?) Serial to Parallel Converter