Browse Prior Art Database

Compatible Scheme to Query Printer Capabilities

IP.com Disclosure Number: IPCOM000036215D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 15K

Publishing Venue

IBM

Related People

Marks, LV: AUTHOR

Abstract

Disclosed is a technique for querying the capabilities of a standard printer over the standard parallel interface. The technique is based on using a constant 'escape sequence' prefix preceding normal printer commands to indicate that datastream is a query. The scheme is compatible and can be used with any parallel printer without setting undesired printer modes.

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Compatible Scheme to Query Printer Capabilities

Disclosed is a technique for querying the capabilities of a standard printer over the standard parallel interface. The technique is based on using a constant 'escape sequence' prefix preceding normal printer commands to indicate that datastream is a query. The scheme is compatible and can be used with any parallel printer without setting undesired printer modes.

It is frequently necessary for software preparing data for a printer to know the printer's capabilities.

The problem is complicated by the 'parallel' interface in common use today. Although that interface can control the printer, there is very little facility for getting information from the printer. Only one or two signal lines are available.

The solution currently in use involves sending a Query Escape sequence to the printer, of the form Esc Q nn, which effectively asks the printer, "Are you printer ID nn?" The printer responds only to the correct ID by changing its selection state to 'Deselected,' and indicating this on a signal line of the parallel interface. This is not an adequate solution because:

1) The software must successively query all known printer ID values until a match is found;

2) The software must contain an up-to-date table associating ID numbers with capabilities; and

3) This approach makes no allowance for printer options.

There is a standard set of printer codes used to invoke advanced functions; for example, Esc E sets emphasized mode, Esc J nn advances the paper a variable distance, etc. A desirable solution would provide the ability for the software to ask (query) the printer to see if it has the required capabilities; for example, to ask "Do you support Esc E?" or "Do you support Esc J?"

Another consideration is conservation of codes. There are a limited set of Esc code points available. A solution that used a large number of them, one to query each feature, would not be attractive.

Another consideration is compatibility. It can be undesirable to invent new printer sequences and send them to old printers, unless it can be guaranteed that the old printer can successfully discard those sequences. The old printer must be able to figure out the length of the new sequence and discard exactly that length. If it discards too many bytes, information (characters or the beginning of subsequent control sequences) is lost. If too few bytes are discarded, parametric data pertaining to the unsupported new command are interpreted as separate commands or characters to be printed. This usually works correctly, because, in addition to using a standardized base set of codes, IBM printers all use the same set of code formation rules, so even when a printer receives an unrecognized new code, it can correctly determine that code's length.

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Description of Invention: A code query sequence that meets the criteria above ca...