M16C/26 Group
2. CPU
2. Central Processing Unit (CPU)
Figure 2.1 shows the CPU registers. The CPU has 13 registers. Of these, R0, R1, R2, R3, A0, A1 and FB
comprise a register bank. There are two register banks.
b31
b15
b8b7
b0
R2
R3
R0H(R0's high bits) R0L(R0's low bits)
R1H(R1's high bits)R1L(R1's low bits)
Data registers (Note)
R2
R3
A0
A1
FB
Address registers (Note)
Frame base registers (Note)
b19
b15
b0
INTBH
INTBL
Interrupt table register
Program counter
The upper 4 bits of INTB are INTBH and
the lower 16 bits of INTB are INTBL.
b19
b0
b0
PC
b15
USP
User stack pointer
Interrupt stack pointer
Static base register
ISP
SB
b15
b0
b0
FLG
Flag register
b15
b8 b7
IPL
U
I O B S Z D C
Carry flag
Debug flag
Zero flag
Sign flag
Register bank select flag
Overflow flag
Interrupt enable flag
Stack pointer select flag
Reserved area
Processor interrupt priority level
Reserved area
Note: These registers comprise a register bank. There are two register banks.
Figure 2.1. Central Processing Unit Register
2.1 Data Registers (R0, R1, R2 and R3)
The R0 register consists of 16 bits, and is used mainly for transfers and arithmetic/logic operations. R1 to
R3 are the same as R0.
The R0 register can be separated between high (R0H) and low (R0L) for use as two 8-bit data registers.
R1H and R1L are the same as R0H and R0L. Conversely, R2 and R0 can be combined for use as a 32-bit
data register (R2R0). R3R1 is the same as R2R0.
2.2 Address Registers (A0 and A1)
The register A0 consists of 16 bits, and is used for address register indirect addressing and address regis-
ter relative addressing. They also are used for transfers and logic/logic operations. A1 is the same as A0.
In some instructions, registers A1 and A0 can be combined for use as a 32-bit address register (A1A0).
Rev.1.00 2004.6.10 page 9 of 37
REJ09B0176-0100Z
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