Usage of PAP for inkjet printers

[robin-fo]

To procrastinate some things I had to do yesterday, I pulled the User's manual of the original HP DeskWriter out of my bookshelf. To my surprise, I realized that this printer can a) use AppleTalk networking, b) can autodetect the presence of LocalTalk dongles and automatically switch between serial and network communication and c) doesn't use ADSP for AppleTalk communication, but, like the LaserWriters, uses PAP. This last point really astonished me. Up to now, I thought non-PostScript AppleTalk printers just tunnel their serial communication protocol through ADSP (which, like TCP, allows UART-like communication over the network).

I now wonder if there are any (other?) documented uses of PAP with other protocols/languages than PostScript.. Or is the DeskWriter maybe really using PostScript for printing?

 

[NJRoadfan]

I suspect most everyone used PAP. My EPSON Stylus Color 900N spoke ESCP/2 and used PAP via its EPSON Type B network card. My HP LaserJets will all accept PCL via PAP as well. They just see the PCL magic string or PJL header and do language switching based on that. The DeskWriters are using PCL3c, just like their DeskJet cousins.

The most oddball and buggy implementation is the ImageWriter II/LQ card. It sends out a 2 byte value as a PAPStatus message instead of human readable text. The driver is expected to parse the bit values to figure out the installed printer options and status.

PAP itself is just a bidirectional pipe to a printer. Many platforms treat it similar to parallel port printers and just transmit data to the printer, not doing any interactive communication like the LaserWriter drivers do. The Windows Services For AppleTalk handles printers like this. PAP handles the flow control if there is a printer stoppage (see Inside AppleTalk). The client does NOT rely on PAPStatus messages for this.

 

[robin-fo]

That‘s interesting, many thanks! Perhaps ADSP is only used for printers which do not natively support AppleTalk, like the StyleWriters..?

 

[NJRoadfan]

Which setup is using ADSP? Is it the GrayShare/ColorShare software and/or the StyleWriter LocalTalk and EtherTalk connection boxes?

 

[robin-fo]

I know for sure that the StyleWriter II Printer Sharing extension* uses ADSP, as well as the lpstyl software for BSD which supports many StyleWriters and Color StyleWriters. So It‘s probably safe to assume that also the StyleWriter-to-LocalTalk/EtherTalk dongles used ADSP.

* I guess this is the same as the GrayShare you mentioned.

I have one of these (https://www.ebay.ch/itm/31500692966...3-7ygrpska&var=&widget_ver=artemis&media=COPY) but never tested it. Perhaps it‘s time to search for new cartridges for my CSW 2400..

 

[NJRoadfan]

I'd still like to know why Apple went the route of using ADSP vs. the established PAP for these. A few possible (likely wrong) reasons:

-The printer's communication with the host couldn't easily support PAP. Looking at the notes on the lpstyl driver shows that these printers are really fussy about data flow and don't recover easily from errors or overflows. This would make sense for the simple network adapters, but ColorShare/GrayShare would be able to handle all this easily on a host Macintosh.
-Apple wanted something simple and easily reuse as much of the existing driver code on a Mac as possible.
-Apple wanted to purposely cripple the network ability of these printers. PAP being well established already had a large ecosystem of spoolers and other network tools.

 

[cheesestraws]

-Apple wanted something simple and easily reuse as much of the existing driver code on a Mac as possible.

simple and cheap. And perhaps to be built by engineers who weren't printing gurus. This would be my bet.