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I know that a LPT port is capable of bi-directional communication. It is obvious that PC will send data to printer, but is the reverse true? Will the PC read data from the printer at any time? I can imagine that reading status/error codes/manufacturer info etc. would be useful.

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The typical printer will sends its status using the Centronics interface back to the host. But normally status is not considered data. The typical printer only receives data from the host PC. IIRC Unix assigned the /dev/lpt device to be write-only. But since the Centronics interface evolved into 2 bi-directional interfaces, I'd assume somewhere there are printers that pushed for and utilized this bi-directional data capability. Maybe to send expanded reports (e.g. available fonts) or upload fonts from cartridges? There were some scanners that used the parallel interface. –  sawdust Sep 8 '12 at 19:14
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2 Answers

Wikipedia offers information on the bi-directionality of LPT ports.

http://en.wikipedia.org/wiki/Parallel_port

Referring to the Pinouts section, it shows that there are eight outbound data line and five inbound status lines. So yes, it can be made bi-directional, but at half-speed for inbound data.

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yes, I understand that LPT is bidirectional. My question was if this capability is actually used at any time for reading data from printer. –  user157081 Sep 8 '12 at 7:47
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Absolutely the PC gets data from the printer. How else would your PC know that the printer is jammed, out of paper, ink, or toner. Even older printers (RS232) were multifunction devices, doing both faxing and scanning. Bidirection communication with the printer was there.

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Status is not the same as data. Even the Centronics (aka LPT) interface makes this distinction. –  sawdust Sep 8 '12 at 18:45
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