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C00002 00002	.IODEVICE( VRN,350,|Varian Plotter and Interface|)
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.IODEVICE( VRN,350,|Varian Plotter and Interface|)


The Varian Statos model 4224 plotter makes plots on 22" wide paper, using
coated paper and an electrostatic process.  This plotter features very
good linearity (especially across the paper), and a very wide plotting
bed.  The Varian's primary drawback is that it requires coated paper.
Coated paper doesn't feel as wonderful as plain paper, is expensive (by
XGP standards), suffers occasionaly from poor contrast, and is not as
universally suitable as plain (XGP) paper.  It has a resolution of 200
pixels per inch, with a 21.12 inch wide plotting bed, giving an effective
width of 4224 pixels.  The paper comes on 500 foot rolls, so there is
little restriction on the length of a plot.

The primary function of the interface is to take a 36 bit word from the
host processor (currently a KA-10), unpack it, and to send it to the
Varian as four nine-bit bytes.

18:29	777700	unused
30	000040	VTEST	Test	(described below)
31	000020	unused  
32	000010	VPIENB  Interrupt enable
33:35	000007	VPIMSK  PI channel assignment

18:19	600000	unused
20	100000	VSDONE	Video scan complete
21	040000	VNOTOK	The Varian is not ready for some reason or other
22	020000	VBFBSY	The line buffer is busy
23	010000	VPCBSY	Paper controller is busy
24	004000	VBTFRM	Bottom of form (unused)
25	002000	unused	
26	001000	VRDRDY	Read ready
27	000400	VOFFLN	Not on-line (i.e., off-line)
28	000200	VSUPLO	Supplies low
29	000100	VVDBSY  Video busy
30	000040	unused	
31	000020	VDATRQ  Data request (cleared by any DATAO)
32	000010	VPIENB  The Varian in interrupting
33:35	000007	VPIMSK  PI channel assignment


The interface takes a 36-bit DATAO word, and sends it to the Varian as four
9-bit bytes.
Each byte is either 'printing data' (400 bit off) or 'command data' (400 bit on).
Here are the commands that the Varian understands:

500	VCMCGS	;Character generator select ("default on reset")
560	VCMMUX	;Select character generator in MUX mode
740	VCMRAS	;Raster write select
644	VCMRAA	;Autostep raster write select (comes on automatically???)
445	VCMCLA	;Autostep mode reset (undoes VCMRAA)
443	VCMLF	;Line sync/step (print buffer and advance paper)
663	;VCMFF	;Form feed ("no-op on 22 inch wide paper")
400	VCMNOP	;No-op for clearing VDATRQ and for padding DATAO words.
464	VCMSTP	;Step (print buffer and advance paper)
665	;VCMSLW	;Slew (advance paper 8.5" to bring last line printed into view)

For diagnostic purposes, this instruction reads in the current contents of the
data buffer.  If the plotter is running, the data in the buffer will be constantly
changing as the data is shipped out to the plotter, in which case this instruction
doesn't make much sense.

The interface has an internal shift register which it uses to unpack
36-bit words into four 9-bit bytes.  Setting the TEST bit in the CONO word
makes the interface go through the internal gyrations of shifting the data
over nine bits, just as it would if it were sending data to the Varian.
If you suspect someting is wrong with the data path of the interface, you
can test it by doing:

	DATAO VRN,[some data]
	DATAI VRN,[some cell]

The data you find in [some cell] should be the data you had in [some data],
but shifted over nine bits.

The Varian interface lives in the P2 TTL-IOBus Extension, built on two of the
ubiquitous DEC W943 wire wrap modules.



(Aside from running out of paper, toner, or concentrate)

Sometimes the paper skews to one side, gets wrinkled, or has dropouts
in printing.  This is probably due to uneven pinch roller pressure.
Remove the front door, and look for two little holes, about 3/4" diameter,
on the left and right hand edges of the face.  Inside are phillips head
screws that control the pinch roller pressure.

Assuming that the paper is skewing to the left, tighten the screw on the
left side about a turn.  (Yes, tighten the right hand screw if the paper
skews to the right.)  Open the platen and straighten out the paper by
pulling out a foot or so.  Close the platen.  Then try running some paper
for several feet while watching for evidence of further skewing.  Repeat
these steps until the paper runs straight.  You may have to loosen the
screws at some point, rather than tighten them.

Often, a new roll of paper will hit the top of the case, causing it
to bind and slip.  No cure is known except to waste some paper by
loosening the platen and pulling the paper out by hand.

Varian "Service and Maintenance Manual for Statos 41/42 Series Printer/Plotters."