Q67120-C0581 查看數據表（PDF） - Siemens AG

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Q67120-C0581

8-Bit CMOS Single-Chip Microcontroller Family

Siemens AG 

Memory Organization

The register XPAGE provides the upper address byte for accesses to XRAM with MOVX @Ri

instructions. If the address formed from XPAGE and Ri is less than the XRAM address range, then

an external access is performed. For the SAB 80C515A the contents of XPAGE must be greater or

equal than F8H in order to use the XRAM. Of course, the XRAM must be enabled if it shall be used

with MOVX @Ri instructions.

Thus, the register XPAGE is used for addressing of the XRAM; additionally its contents are used

for generating the internal XRAM select. If the contents of XPAGE is less than the XRAM address

range then an external bus access is performed where the upper address byte is provided by P2

and not by XPAGE!

Therefore, the software has to distinguish two cases, if the MOVX @Ri instructions with paging shall

be used:

a) Access to XRAM:

The upper address byte must be written to XPAGE or P2;

both writes selects the XRAM address range.

b) Access to external memory: The upper address byte must be written to P2; XPAGE

will be loaded with the same address in order to deselect the XRAM.

The behaviour of Port0, Port2 and the RD/WR signals depends on the state of pin EA and on the

control bits XMAP0 and XMAP1 in register SYSCON.

Semiconductor Group

3-13

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