MODES OF OPERATION

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There are two basic modes of operation, which are selectable by a single bit, FLAG,#0. If this bit is reset, program runs at full-screen mode, using 95,6% processor time and leaving only 4,4% for user's program. Setting this bit puts the program at pure text mode, in which the processor is occupied 77% of the time. Both modes enable using of frame pseudographics and background colours, but in the pure text mode the first 6 scan lines of each text row are unconditionaly forced to black (12 scan lines if that text row is in double height mode).

The main program can set/reset bit FLAG,#0 at any time, but the interrupt routine will copy its state to the bit FLAG,#8 at the beginning of the vertical sync pulse, and use that bit for mode branching in the routine. So, bit FLAG,#8 is internally used for synchronization and should not be modified by the user.
 

FLAG,#0 = 0

  FLAG,#0 = 1

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