AppleTalk #9
The PAP Status Buffer

Written by Jim Luther (November 1990)

This Technical Note shows the format of the status data returned into the application-supplied status buffer by the PAPStatus and PAPOpen Printer Access Protocol (PAP) AppleTalk commands. The status buffer format is shown for both LaserWriter and ImageWriter (with the ImageWriter II/LQ LocalTalk Option card installed) printers.

The PAPStatus and PAPOpen AppleTalk commands must supply a pointer to a 260-byte status buffer. When the PAPStatus or PAPOpen commands complete, the status buffer contains the ATP data portion of a Status (TResp) packet. The first four bytes of that data are unused, so the actual status data starts at offset $04 in the status buffer.

The LaserWriter printer returns its status data in the form of a Pascal string. That string is usually something suitable to display on the screen (e.g., "status: idle" or "job: Fred; document: My LaserWriter is on fire; status: busy; source: AppleTalk"). In fact, the status text displayed in the Print Manager LaserWriter dialog boxes is usually the statusString returned by PAPStatus or PAPOpen. Figure 1 shows the contents of the status buffer returned by a LaserWriter.

          +-------------------+
     $00  |_                 _|    Longword       Unused
          |_      unused     _|
          |_                 _|
          |                   |
          +-------------------+
     $04  |_ (string length) _|
          |_                 _|
          |_                 _|
          .                   .
          .   status string   .    String         The PAP status string
          .                   .                   (Pascal string, ASCII,
          |_                 _|                   high-bit clear)
          |_                 _|
          |                   |
     $103 +-------------------+         
          

                Figure 1 - PAP Status Buffer from a LaserWriter

The ImageWriter II/LQ LocalTalk Option card does not return a status string for display. Instead, it returns a statusBits word where each bit within that word has a specific meaning. Your application can interpret the statusBits word and generate an appropriate message to display. Figure 2 shows the contents of the status buffer returned by the ImageWriter II/LQ LocalTalk Option card and the individual bit definitions of the statusBits word.

          +------------------+
     $00  |_                _|     Longword       Unused
          |_      unused    _|
          |_                _|
          |                  |
          +------------------+
     $04  |string data length|     Byte           Always = 2
          +------------------+
     $05  |_    statusBits  _|     Word           Status bits returned by
          |                  |                    LocalTalk ImageWriter
          +------------------+                    Option card (see following
     $07  |_                _|                    definition)
          |_                _|
          |_                _|
          .                  .     253 Bytes      Unused
          .                  .
          .                  .
          |_                _|                    
          |_                _|
          |                  |
     $103 +------------------+          
     
                            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                            |15|14|13|12|11|10| 9| 8| 7| 6| 5| 4| 3| 2| 1| 0|
                            +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                              |  |<-- Reserved --->|  |  |  |  |  |  |  |  |
1 = Printer is busy ----------+  |_________________|  |  |  |  |  |  |  |  |
                                                      |  |  |  |  |  |  |  |
1 = Color ribbon installed ---------------------------+  |  |  |  |  |  |  |
1 = Sheet feeder installed ------------------------------+  |  |  |  |  |  |
1 = Paper out error ----------------------------------------+  |  |  |  |  |
1 = Cover open error ------------------------------------------+  |  |  |  |
1 = Printer off line ---------------------------------------------+  |  |  |
1 = Paper jam error -------------------------------------------------+  |  |
1 = Printer fault ------------------------------------------------------+  |
1 = Printer active (head is moving) ---------------------------------------+


 Figure 2 - PAP Status Buffer from an ImageWriter II/LQ LocalTalk Option Card

There are two additional things to note when interpreting the statusBits word returned by a ImageWriter II/LQ LocalTalk Option card:

• If a sheet feeder is installed (bit 6 = 1), running out of paper results in a "Paper jam error" (bit 2 = 1) instead of a "Paper out error" (bit 5).
• The ImageWriter II/LQ LocalTalk Option card has been known to randomly return all ones in the low byte (bits 0-7) of the statusBits word. When this happens, the statusBits word is invalid and an application should repeat the PAPStatus call to get valid information.

Further Reference

• Inside AppleTalk, Second Edition
• AppleShare Programmer's Guide for the Apple II Family

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