MIT UNIBUS XGP interface - Revision history

Jnc: Based on the CMU one?

2024-02-27T11:30:57Z

Based on the CMU one?

Jnc: Definitely an -11/20

2024-02-03T20:46:30Z

Definitely an -11/20

Jnc: Add image

2024-02-03T15:43:40Z

Add image

Larsbrinkhoff: /* Data encoding */ For f's sake.

2024-02-02T06:34:04Z

‎Data encoding: For f's sake.

Larsbrinkhoff: /* Data encoding */ Update per the XCRIBL document.

2024-02-01T06:11:39Z

‎Data encoding: Update per the XCRIBL document.

Larsbrinkhoff: Format of encoded data.

2024-01-31T06:07:47Z

Format of encoded data.

Jnc: /* External links */ +XCRIBL - A Hardcopy Scan Line Graphics System for Document Generation

2023-09-15T18:33:01Z

‎External links: +XCRIBL - A Hardcopy Scan Line Graphics System for Document Generation

Jnc: Load Memory Address Register; typo in vector

2023-09-14T17:18:38Z

Load Memory Address Register; typo in vector

Jnc: typo

2023-09-14T15:02:46Z

typo

Jnc: Interrupts; the XGP-11 code handles raster line in buffer header (see XGPD1:)

2023-09-14T15:01:39Z

Interrupts; the XGP-11 code handles raster line in buffer header (see XGPD1:)

@@ Line 14: / Line 14: @@
 To print a scan line, load the Memory Address Register (below), set the FGO and FMOT bits in the Control Register (ditto); FDIE as well, to get an [[interrupt]] when done. The interface's [[interrupt vector]] is 0370.
-The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT connected theirs to a [[PDP-11/20]] (there was at one point some confusion about exactly which model of [[PDP-11]] it was, some thought it was a [[PDP-11/05]]; the discovery of the image confirms that it was an -11/20). That was connected to the [[Incompatible Timesharing System|ITS]] [[KA10]] MIT-AI via the [[Rubin 10-11 interface]].
+The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT and Carnegie-Mellon both used PDP-11's to drive their XGP's, but it is not known how much there was any design connection between the two interfaces (although the similarity of the specifications of the two makes it plausible that there was some knowledge exchange).
 ==Device registers==

@@ Line 14: / Line 14: @@
 To print a scan line, load the Memory Address Register (below), set the FGO and FMOT bits in the Control Register (ditto); FDIE as well, to get an [[interrupt]] when done. The interface's [[interrupt vector]] is 0370.
-The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT connected theirs to a [[PDP-11/20]] (there is some confusion about exactly which model of [[PDP-11]] it was, some think it was [[PDP-11/05]]). That was connected to the [[Incompatible Timesharing System|ITS]] [[KA10]] MIT-AI via the [[Rubin 10-11 interface]].
+The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT connected theirs to a [[PDP-11/20]] (there was at one point some confusion about exactly which model of [[PDP-11]] it was, some thought it was a [[PDP-11/05]]; the discovery of the image confirms that it was an -11/20). That was connected to the [[Incompatible Timesharing System|ITS]] [[KA10]] MIT-AI via the [[Rubin 10-11 interface]].
 ==Device registers==

@@ Line 1: / Line 1: @@
 The '''MIT UNIBUS XGP interface''' was a one-off [[UNIBUS]] [[peripheral]] which drove a [[Xerox Graphics Printer]], the earliest [[raster]] [[printer]] (and thus the ancestor of the ubiquitous [[laser printer]]).
@@ Line 58: / Line 60: @@
 The data pointed to by XMAR is DMA'd from memory and decoded by the interface in various modes.  For each fresh line, the interface starts off in ''character'' mode.
-In character mode, the first byte says how many bits of data follow.  Subsequent bytes are shifted to the video flip-flop controlling the CRT beam, as many as necessary to reach the bit count.  A '''0''' byte escapes character mode.  The next byte decides what mode to switch to: '''0''' enters ''vector'' mode.  '''1''' stops the printer and sets DONE.  '''2''' enters ''image'' mode.  Anything else is an error.
+In character mode, the first byte says how many bits of data follow.  Subsequent bytes are shifted to the video flip-flop controlling the CRT beam, as many as necessary to reach the bit count.  A '''0''' byte escapes character mode.  The next byte decides what mode to switch to: '''0''' enters ''vector'' mode; '''1''' stops the printer and sets DONE; '''2''' enters ''image'' mode.  Anything else is an error.
 In vector mode, alternating bytes say how many pixels of white or black to draw.  Two zeros in succession escapes back to character mode.
@@ Line 68: / Line 70: @@
 * [https://github.com/PDP-10/its/blob/master/src/sysen2/xgp.32 SYSEN2; XGP >] - code to run the interface
 * [https://github.com/PDP-10/its/blob/master/doc/info/xgp.24 INFO; XGP >] - documentation on the spooler, and the input file format
 * [http://shelf2.library.cmu.edu/Tech/backups/227003483.pdf XCRIBL - A Hardcopy Scan Line Graphics System for Document Generation] - a fair amount of detail on the CMU system
 * [https://www.ietf.org/rfc/rfc320.txt Workshop on Hard Copy Line Graphics] - details of the XGP installation at CMU
 [[Category: UNIBUS Peripherals]]
 [[Category: Printers]]

← Older revision		Revision as of 06:34, 2 February 2024
Line 55:		Line 55:

	==Data encoding==		==Data encoding==
−	f	+
	The data pointed to by XMAR is DMA'd from memory and decoded by the interface in various modes. For each fresh line, the interface starts off in ''character'' mode.		The data pointed to by XMAR is DMA'd from memory and decoded by the interface in various modes. For each fresh line, the interface starts off in ''character'' mode.

@@ Line 55: / Line 55: @@
 ==Data encoding==
-The data pointed to by XMAR is encoded, but the format is not yet fully understood.  The printer starts of in ''command'' or ''character'' mode.
+In character mode, the first byte says how many bits of data follow.  Subsequent bytes are shifted to the video flip-flop controlling the CRT beam, as many as necessary to reach the bit count.  A '''0''' byte escapes character mode.  The next byte decides what mode to switch to: '''0''' enters ''vector'' mode.  '''1''' stops the printer and sets DONE.  '''2''' enters ''image'' mode.  Anything else is an error.
-A '''0''' byte escapes command mode.  The next byte decides what mode to switch to: '''0''' enters run-length encoded mode.  '''1''' stops the printer.  '''2''' enters image mode.  Anything else is an error.
+In vector mode, alternating bytes say how many pixels of white or black to draw.  Two zeros in succession escapes back to character mode.
-In RLE mode, alternating bytes say how many pixels of white or black to draw.  Two zeros in succession exits to command mode.
+In image mode, bytes are imaged to pixels verbatim.  There is no escape except an error condition.  Normally this will be an overscan error when the beam reaches the right margin.
 ==External links==

@@ Line 53: / Line 53: @@
 | colspan=13 | Unused || FCUTI || colspan=2 | Unused
 {{16bitoctal-bitout}}
 ==External links==

@@ Line 10: / Line 10: @@
 It is not yet clear if this last is interpreted by the hardware, or the driver in the PDP-11.
-To start printing a scan line, FGO and FMOT bits are set in the Control Register (below); FDIE as well, to get an [[interrupt]] when done. The interface's [[interrupt vector]] is 070.
+To print a scan line, load the Memory Address Register (below), set the FGO and FMOT bits in the Control Register (ditto); FDIE as well, to get an [[interrupt]] when done. The interface's [[interrupt vector]] is 0370.
 The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT connected theirs to a [[PDP-11/20]] (there is some confusion about exactly which model of [[PDP-11]] it was, some think it was [[PDP-11/05]]). That was connected to the [[Incompatible Timesharing System|ITS]] [[KA10]] MIT-AI via the [[Rubin 10-11 interface]].

@@ Line 5: / Line 5: @@
   "Each [scan] line consists of a header, specifying how long it is, which line it is to be printed upon, and options .. These two words of header are followed by the line in the format required by the XGP interface.
   The first PDP-11 word in each line is the number of PDP-11 WORDS .. used for this scan line, including itself and the rest of the header. [The buffer length appears to be in byte-swapped order.] ..
-  The second PDP-11 word is the scan line upon which this line is to be printed. [It is not clear if this in interpreted by the hardware, or the driver in the PDP-11.] It is allowable to have non-sequential lines. The unspecified lines will be blank. If the line numbers are not ordered, they will come out as close as possible together, and the internal line count will be reset. .. The top line on a page is numbered 1. ..
+  The second PDP-11 word is the scan line upon which this line is to be printed. [It is not clear if this in interpreted by the hardware as well, or just by the driver in the PDP-11.] It is allowable to have non-sequential lines. The unspecified lines will be blank. If the line numbers are not ordered, they will come out as close as possible together, and the internal line count will be reset. .. The top line on a page is numbered 1. ..
   Paper cutting may be specified by setting the sign [high bit] of the second PDP-11 word. The rest of the [scan line] so marked will be ignored"
 It is not yet clear if this last is interpreted by the hardware, or the driver in the PDP-11.
 The XGP at [[Massachusetts Institute of Technology|MIT]] was one of a number provided to various entities by [[Xerox]] in 1972; each had to produce its own hardware computer interfaces. MIT connected theirs to a [[PDP-11/20]] (there is some confusion about exactly which model of [[PDP-11]] it was, some think it was [[PDP-11/05]]). That was connected to the [[Incompatible Timesharing System|ITS]] [[KA10]] MIT-AI via the [[Rubin 10-11 interface]].