Zilog Z8F0130 Manual de usuario Pagina 53

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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.
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