Table of Contents
Advertisement
Downloaded from
Elcodis.com
electronic components distributor
2.6.5 Notes on Use of Bit Manipulation Instructions
The BSET, BCLR, BNOT, BST, and BIST instructions read a byte of data, modify a bit in the
byte, then write the byte back. Care is required when these instructions are used to access registers
with write-only bits, or to access ports.
The BCLR instruction can be used to clear flags in the on-chip registers. In an interrupt-handling
routine, for example, if it is known that the flag is set to 1, it is not necessary to read the flag
ahead of time.
2.7 Addressing Modes and Effective Address Calculation
2.7.1 Addressing Modes
The H8/300H CPU supports the eight addressing modes listed in table 2-11. Each instruction uses
a subset of these addressing modes. Arithmetic and logic instructions can use the register direct
and immediate modes. Data transfer instructions can use all addressing modes except program-
counter relative and memory indirect. Bit manipulation instructions use register direct, register
indirect, or absolute (@aa:8) addressing mode to specify an operand, and register direct (BSET,
BCLR, BNOT, and BTST instructions) or immediate (3-bit) addressing mode to specify a bit
number in the operand.
Table 2-11 Addressing Modes
No.
Addressing Mode
1
Register direct
2
Register indirect
3
Register indirect with displacement
4
Register indirect with post-increment
Register indirect with pre-decrement
5
Absolute address
6
Immediate
7
Program-counter relative
8
Memory indirect
Symbol
Rn
@ERn
@(d:16, ERn)/@d:24, ERn)
@ERn+
@–ERn
@aa:8/@aa:16/@aa:24
#xx:8/#xx:16/#xx:32
@(d:8, PC)/@(d:16, PC)
@@aa:8
39
Advertisement
Table of Contents
