Structure of display file in vector refresh display

In Vector display system a display file is used to store the instructions to draw lines. Algorithms are used to read and apply these display files for the output.

There are two fields in a display file command; one is the opcode (operation code) and operands. Opcode is used for the identification of the command where in the operands are used to determine the coordinates of a point. Opcodes needs to be defined before the operation:

Command Opcode
Plot 1
Move 2
Line 3

Now, since the opcodes are defined, now we can write an algorithm to give commands to display file:

1)      Read opcode (x,y)

2)      I -> empty row

3)      D_OP[i] -> opcode

4)      D_x[i] -> x

5)      D_y[i] ->y

6)      Stop


D_OP D_x D_y
2 20 20
3 60 60

Now, when we execute: 2, 20, 20: The cursor is moved to location (20,20):

After that we execute 3,60, 60: Draw a line to (60,60):


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