SC4020 Instructions
Opcode
in Octal		 Format Name Operation
00 1 PLOT Plot C at (X,Y)
02 1 EXPOSE HEAVY Set to Expose Heavy Mode. Plot C at (X,Y)
04 1 EXPOSE LIGHT Set to Expose Light Mode. Plot C at (X,Y)
06 6 DRAW VECTOR vector (X,Y,X+SX*DX,Y-SY*DY);
SX=+1 if bit 18 =1 else -1;
SY=+1 if bit 19 =1 else -1;
07 2 IGNORE REST OF RECORD
12 2 STOP TYPE Return to Plotting Mode
20 1 TYPE SPECIFIED POINT Type C at (X,Y). Enter Typing Mode
22 5 TYPE CURRENT POINT Type Ci from current point. Enter Typing Mode
30 3 GENERATE X AXIS vector(X,Y,I,Y) where I=complement(S)
32 3 GENERATE Y AXIS vector(X,Y,X,S)
37 2 STOP SC4020
41 2 SELECT MF CAMERA
42 2 SELECT HC CAMERA
43 2 SELECT BOTH CAMERAS
44 2 EXPAND IMAGE
45 2 REDUCE IMAGE
46 4 ADVANCE FILM Advance Film if I=0
46 4 ADVANCE REPEAT Advance Film and repeat N times if I=1
50 2 PROJECT FORM
56 2 RESET Equivalent to Advance Film, Stop typing, Expose heavy

The SC4020 order code consisted of single 36-bit word instructions in seven different instruction formats. The addresses are with respect to the SC4020's 1024 by 1024 plotting area.

TYPE 1 05 OPCODE 67 817 X 1823 C 2425 2635 Y TYPE 2 05 OPCODE 635 TYPE 3 05 OPCODE 67 St 817 X 1825 Sb 2635 Y TYPE 4 05 OPCODE 611 1217 N 1822 23 I 2435 TYPE 5 05 OPCODE 611 C1 1217 C2 1823 C3 2429 C4 3035 C5 TYPE 6 01 11 27 DX 817 X 18 SX 19 SY 2025 DY 2635 Y TYPE 7 05 C1 611 C2 1217 C3 1823 C4 2429 C5 3035 C6

The origin of the coordinate system is upper left corner. Positive Y is downwards. Any character can be plotted at any of the addressable positions (0,0) to (1023,1023).

About 350 lines can be resolved out of the 1000 addressable positions.

Some details about the order code:

  • 00: plot character
  • 02: expose heavy and plot character, remains set to heavy
  • 04: expose light and plot character, remains set to light
  • 06: draw vector from point specified to point DX,DY away in light exposure
  • 20: type character at specified point, subsequent characters in this mode will appear in subsequent character positions
  • 22: type character at specified point and the one to the right, should be followed by words packed 6 characters per word that continue the printing until right hand margin when a carriage return (52) is initiated. The character SOP 12 (stop print) will terminate typewriter mode. The character RES (56) initiates STOP PRINT, ADV FILM, EXPOSE HEAVY
  • 30 32 draws an axis from the specified position to the right (X=1023) or top (Y=0) coordinate:
  • 41: opens the shutter of the microfilm camera
  • 42: opens the shutter of the hardcopy camera
  • 43: opens the shutter of both cameras
  • 46: advance film in the selected cameras, resets the beam to X=0, Y=0
  • 56: causes advance film and stop print. Exposure reset to normal (heavy)