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Semiconductor Group 3 - 13

Memory Organization

Figure 3-4

Use of Port 2 as I/O-Port

At a write to Port 2, XRAM address in XPAGE-register will be overwritten because of the concurrent

write to Port 2 and XPAGE-register. So whenever XRAM is used and the XRAM address differs

from the byte written to Port 2 latch it is absolutely nessesary to rewrite XPAGE with page address.

Example:

I/O-Data at Port 2 shall be 0AAH. A Byte shall be fetched from XRAM at address 0F830

MOV R0, #30H

MOV P2, #0AAH ; P2 shows 0AA

MOV XPAGE, #0F8H ; P2 still shows 0AA

but XRAM is addressed

MOVX A, @R0 ; the contents of XRAM at 0F830

is moved to accu

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