Figure 2.1.2B General-Purpose Registers; Figure 2.1.2C Program Counter - Fujitsu F2MC-16LX MB90580 Series Hardware Manual

General-purpose registers
2
The F MC-16LX general-purpose registers are located from addresses 000180H to 00037FH (maximum
configuration) of main storage. The register bank pointer (RP) indicates which of the above addresses are
currently being used as a register bank. Each bank has the following three types of registers. These
registers are mutually dependent as described in Figure 2.1.2b.
• R0 to R7: 8-bit general-purpose register
• RW0 to RW7: 16-bit general-purpose register
• RL0 to RL3: 32-bit general-purpose register
000180
First address of
general-purpose register
The relationship between the high-order and low-order bytes of a byte or word register is expressed as
follows:
The relationship between the high-order and low-order bytes of Rli and RW can be expressed as follows:
Program counter (PC)
The PC register is a 16-bit counter that indicates the low-order 16 bits of the memory address of an
instruction code to be executed by the CPU. The high-order eight bits of the address are indicated by the
PCB. The PC register is updated by a conditional branch instruction, subroutine call instruction, interrupt,
or reset.
The PC register can also be used as a base pointer for operand access.
PCB FE
MB90580 Series
+ RP*10
H H
Low-order
High-order

Figure 2.1.2b General-purpose registers

RW = R *256+R
(i+4) (i*2+1)
RL = RW *65536+RW
(i) (i*2+1)
PC
A BCD
H

Figure 2.1.2c Program counter

MSB
16 bit
RW0
RW1
RW2
RW3
R1 R0
R3
R2
R5 R4
R7 R6
[i=0 to 3]
(i*2)
[i=0 to 3]
(i*2)
H
Next instruction to be executed
FEABCD
H
LSB
RL0
RL1
RW4
RL2
RW5
RW6
RL3
RW7
Chapter 2: CPU
2.1 CPU
21