Zilog Z86193 - Manual (Page 21)

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)