| 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 |
see also: