The first step in programming display equipment, in order to produce a picture on the screen, is to generate a stream of binary words. These form a series of commands to the display; each command causing the display to carry out one of its functions, such as: to position the beam; to move it linearly painting a line; or to produce a character. Depending on the make of hardware and the word length, these various types of operation are distinguished by, say, the 4 most significant bits (or by control words which change the subsequent mode of operation) the remainder of the word being the binary values of X and Y, changes in X and Y (each usually to 10 bits), or the codes of 2 or 3 characters.
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