Zilog Z8F0130 - Manual (Page 53)

eZ8
™
CPU Core
User Manual
UM012820-0810 Addressing Modes
31
Escaped Mode Addressing with 8-bit Addresses
Using Escaped Mode Addressing 8-bit addresses can specify a working
register. If the high nibble of the 8-bit address is
Eh ( 1110b ), the lower
nibble indicates the working register and the full 12-bit address is
provided by
{RP[3:0], RP[7:4], Address[3:0]} . For example, if
ECh is the 8-bit address operand, it implies working register R12 at the
address {RP[3:0], RP[7:4], Ch} . Since addresses E0h to EFh are
used for escaped mode addressing, to access registers with these
addresses, either set the Working Group Pointer,
RP[7:4] , to Eh or use
indirect addressing.
Escaped Mode Addressing with 12-bit Addresses
Using Escaped Mode Addressing, address mode ER for the source or des-
tination can specify a working register with 4-bit addressing. If the high
byte of the 12-bit source or destination address is
EEh(11101110b) , the
lower nibble indicates the working register and the full 12-bit address is
provided by
{RP[3:0], RP[7:4], Address[3:0]} . For example,
the operand EE3h selects working register R3. The full 12-bit address is
provided by {RP[3:0], RP[7:4], 3h} .
Using Escaped Mode Addressing, address mode ER for the source or des-
tination can also specify a register with 8-bit addressing. If the high nibble
of the 12-bit source or destination address is
Eh (1110b) , the lower byte
indicates the 8-bit register address and the full 12-bit address is provided
by
{RP[3:0], Address[7:0]} . For example, the operand E13h
selects 8-bit register at address 13h on the page indicated by RP[3:0] .
The full 12-bit address is provided by {RP[3:0], 13h} . This addressing
mode is sometimes referred to as RP-based page addressing.
Since addresses E00h to EFFh are used for escaped mode addressing, to
access registers on page Eh (addresses E00h to EFFh ), set the Page
Pointer, RP[3:0] , to Eh and set the Working Group Pointer, RP[7:4] , to
the preferred Working Group.