Z8
®
CPU
User Manual
UM001604-0108 Address Space
14
Because enabling an ERF Bank (C or F) only changes register addresses 00h to 0Fh, the
working register pointer can be used to access either the selected ERF Bank (Bank C or F,
Working Register Group 0) or the
Z8
®
Standard Register File (ERF Bank 0, Working Reg-
ister Groups 1 through F).
When an ERF Bank other than Bank 0 is enabled, the first 16 bytes of
the Z8 Standard
Register File (I/O ports 0 to 3, Groups 4 to F) are no longer accessible (the selected ERF
Bank, Registers
00h to 0Fh are accessed instead). It is important to re-initialize the Regis-
ter Pointer to enable ERF Bank 0 when these registers are required for use.
The SPI register is mapped into ERF Bank C. Access is easily done using the example in
Table 6.
If R253 RP = FFh
;ERF Bank F, Working Reg.
Group F.
00h = PCON
R0 = SI0 01h = Reserved
R1 = TMR 02h = Reserved
...
R2 = T1 0Bh = SMR
...
R15 = SPL 0Fh = WDTMR
Table 6. ERF Bank C Access Example
LD RP, #0Ch ;Select ERF Bank C working
;register group 0 for access.
LD R2,#xx ;access SCON
LD R1, #xx ;access RXBUF
LD RP, #00h ;Select ERF Bank 0 so I/O ports
;are again accessible.
Table 5. Register Pointer Access Example (Continued)
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