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Purpose: Set the top of RAM Call address: $FF99 (hex) 65433 (decimal) Communication registers: X, Y Preparatory routines: None Error returns: None Stack requirements: 2 Registers affected: X, Y |
Description:
This routine is used to set the top of RAM. When this routine is called with the carry bit of the accumulator set, the pointer to the top of RAM will be loaded into the X and Y registers. When this routine is called with the accumulator carry bit clear, the contents of the X and Y registers are loaded in the top of memory pointer, changing the top of memory.
EXAMPLE:
;DEALLOCATE THE RS-232 BUFFER
SEC
JSR MEMTOP ;READ TOP OF MEMORY
DEX
CLC
JSR MEMTOP ;SET NEW TOP OF MEMORY