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1.1 root 1: .th VT IV 10/22/73
2: .sh NAME
3: vt \*- 11/20 (vt01) interface
4: .sh DESCRIPTION
5: The file
6: .it vt0
7: provides
8: the interface to a PDP 11/20 which
9: runs a VT01A-controlled Tektronix 611
10: storage display.
11: The inter-computer interface is
12: a pair of DR-11C word interfaces.
13: .s3
14: Although the display has essentially only two commands,
15: namely ``erase screen'' and ``display point'', the 11/20 program
16: will draw points, lines, and arcs, and print
17: text on the screen.
18: The 11/20 can also type information
19: on the attached 33 TTY.
20: .s3
21: This special file operates in two basic modes.
22: If the first byte written of the file
23: cannot be interpreted as one of the codes discussed below,
24: the rest of the transmitted
25: information is assumed to ASCII and
26: written on the screen.
27: The screen has 33 lines (1/2 a standard page).
28: The file simulates a 37 TTY: the control characters
29: NL, CR, BS, and TAB are interpreted correctly.
30: It also interprets the usual escape sequences
31: for forward and reverse half-line motion and for
32: full-line reverse.
33: Greek is not available yet.
34: Normally, when the screen is full (i.e. the 34th line is started)
35: the screen is erased before starting a new page.
36: To allow perusal of the displayed text, it is usual to
37: assert bit 0 of the console switches.
38: This causes the program to
39: pause before erasing until this bit is lowered.
40: .s3
41: If the first byte written is recognizable, the display runs in graphic
42: mode.
43: In this case bytes written on the file
44: are interpreted as display
45: commands.
46: Each command consists of a single byte usually followed
47: by parameter bytes.
48: Often the parameter bytes represent
49: points in the plotting area.
50: Each point coordinate consists of 2 bytes
51: interpreted as a 2's complement 16-bit number.
52: The plotting area itself measures (\(+-03777)\*X(\(+-03777)
53: (numbers in octal);
54: that is, 12 bits of precision.
55: Attempts to plot
56: points outside the screen limits are ignored.
57: .s3
58: The graphic commands follow.
59: .s3
60: .lp +10 5
61: order (1); 1 parameter byte
62: .br
63: The parameter indicates a subcommand, possibly followed
64: by subparameter bytes, as follows:
65: .s3
66: .lp +15 5
67: erase (1)
68: .br
69: The screen is erased.
70: The program will wait until
71: bit 0 of the console switches is down.
72: .s3
73: .lp +15 5
74: label (3); several subparameter bytes
75: .fi
76: .br
77: The following bytes up to a null byte are printed
78: as ASCII text on the screen.
79: The origin of the text is the last previous point
80: plotted; or the upper left hand of the screen if there were none.
81: .s3
82: .lp +10 5
83: point (2); 4 parameter bytes
84: .br
85: The 4 parameter bytes are taken as a pair of coordinates
86: representing a point to be plotted.
87: .s3
88: .lp +10 5
89: line (3); 8 parameter bytes
90: .br
91: The parameter bytes are taken as 2 pairs of coordinates
92: representing the ends of a line segment which is plotted.
93: Only the portion lying within the screen is displayed.
94: .s3
95: .lp +10 5
96: frame (4); 1 parameter byte
97: .br
98: The parameter byte is taken as a number of sixtieths of a second;
99: an externally-available lead is asserted for that time.
100: Typically the lead is connected to
101: an automatic camera
102: which advances its film and opens the
103: shutter for the specified time.
104: .s3
105: .lp +10 5
106: circle (5); 6 parameter bytes
107: .br
108: The parameter bytes are taken as a coordinate pair representing
109: the origin, and a word representing the radius of a circle.
110: That portion of the circle which lies within the screen is plotted.
111: .s3
112: .lp +10 5
113: arc (6); 12 parameter bytes
114: .br
115: The first 4 parameter bytes are taken to be a coordinate-pair
116: representing the center of a circle.
117: The next 4 represent a coordinate-pair specifying a point
118: on this circle.
119: The last 4 should represent another point on the
120: circle.
121: An arc is drawn counter-clockwise from the first circle point
122: to the second.
123: If the two points are the same, the whole circle is drawn.
124: For the second point, only the smaller in magnitude
125: of its two coordinates is significant;
126: the other is used only to find the quadrant of the end of the arc.
127: In any event only points within the screen limits are
128: plotted.
129: .s3
130: .lp +10 5
131: dot-line (7); at least 6 parameter bytes
132: .br
133: The first 4 parameter bytes are taken
134: as a coordinate-pair representing the origin
135: of a dot-line.
136: The next byte is taken as a signed
137: x-increment.
138: The next byte is an unsigned word-count,
139: with `0' meaning `256'.
140: The indicated
141: number of words is picked up.
142: For each bit in each word a point is plotted
143: which is visible if the bit is `1', invisible
144: if not.
145: High-order bits are plotted first.
146: Each successive point (or non-point) is offset
147: rightward by the given x-increment.
148: .s3
149: .i0
150: Asserting bit 3 of the console switches
151: causes the display processor to throw away everything written on it.
152: This sometimes helps if the display seems to be hung up.
153: .sh FILES
154: /dev/vt0
155: .sh BUGS
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