Addressing Modes - ZiLOG Z8 PLUS User Manual

ADDRESSING MODES

P
LUS
The Z8 microcontroller provides six addressing modes:
Register (R)
Indirect Register (IR)
Indexed (X)
Direct Address (DA)
Relative Address (RA)
Immediate Data (IM)
With the exception of immediate data and condition codes, all operands are expressed as register file or
Program Memory addresses. Registers are accessed using 12-bit addresses in the range of 000H-FFFH. The
Program Memory is accessed using 16-bit addresses (or register pairs) in the range of 0000H-FFFFH.
Generally, registers are accessed, within the current page, by specifying an 8-bit address. The upper 4 bits of
the absolute address is specified by pre-pending the lower 4 bits of the Register Pointer (0FDH) (the Page
Pointer) to the 8-bit address to form a 12-bit address.
Working Registers are accessed using 4-bit addresses in the range of 0-15 (0H-FH). The address of the
register being accessed is formed by the combination of the lower 4 bits of the RP (Page Pointer), the upper
four bits in the Register Pointer (Group Pointer) and the 4-bit working register address supplied by the instruc-
tion.
Registers can be used in pairs to designate 16-bit values or memory addresses. A Register Pair must be spec-
ified as an even-numbered address in the range of 0–14 for Working Registers, or 0–4094 for general purpose
registers.