The SC4020 order code of 36-bit word instructions was primarily designed to allow the SC4020 to print output on various media as though it were an extremely fast lineprinter.
The seven-inch CHARACTRON cathode ray tube consisted of:
The first set of deflection plates moved the beam to the desired character position in the matrix. The electron beam was extruded through the hole and then had the shape of the hole. The second set of deflection plates positioned the shaped electron beam on to the face of the phosphor screen. Whichever camera was selected had its shutter open and an image of the character formed by the hole was retained before the phosphor image faded away.
The 64 character positions were assigned to the 48 IBM BCD alphanumeric codes augmented by 16 additional codes:
The contents of the charactron mask are:
0 1 2 3 4 5 6 7
8 9 ∂ = " ' δ α
+ A B C D E F G
H I π • ) β ± ?
- J K L M N O P
Q R . $ * γ ∼ d
/ S T U V W X
Y Z ° , ( ∫ Σ □
From the top to bottom by row the codes are octal 00 to 77. The additional 16 codes are:
12 Partial derivative 14 Quote 16 Delta 17 Alpha 32 Pi 35 Beta 36 Plus or Minus 37 Question Mark 52 Plotting Dot 55 Gamma 56 Tilde 57 Differential 72 Degree 75 Integral Sign 76 Sigma 77 Alignment frame
An extruded character is centred on the point specified on the (0,0) to (1023,1023) display area. Each character takes up 8 positions in the X-direction so that 64 lines of 128 characters can be printed. The origin is the top left position and X extends to the right and Y downwards.
TYPE SPECIFIED POINT printed a specified character at the X,Y position given in the command. TYPE CURRENT POINT typed up to 5 characters from the currently specified point and could be followed by words containing a further 6 characters per SC4020 word. Characters were printed on the current line until either the 128th position was reached or the octal 52 code was encountered in typing mode when a carriage return would be generated to the start of the next line (X=0).
The STOP TYPE or RESET commands returned the SC4020 to Plotting (drawing) mode. If a sequence of characters in several words were output, the appearance of a partial derivative character (octal 12) or tilde (octal 52) would return the SC4020 to plotting mode.