Dedicated Registers; Figure 3.2-1 Dedicated Register Configuration - Fujitsu F2MC-8L Series Hardware Manual

CHAPTER 3 CPU
3.2

Dedicated Registers

The dedicated registers in the CPU consist of the program counter (PC), two arithmetic
operation registers (A and T), three address pointers (IX, EP, and SP), and the program
status (PS). All registers are 16 bits.
Dedicated Register Configuration
The dedicated registers in the CPU consist of seven 16-bit registers. Some of these registers
are also able to be used as 8-bit registers, using the lower 8 bits only.
Figure 3.2-1 shows the structure of the dedicated registers.
Initial value
FFFD
H
Indeterminate
Indeterminate
Indeterminate
Indeterminate
Indeterminate
I-flag = "0",
IL0, IL1 = "11"
Other bits are indeterminate.
Dedicated Register Functions
Program counter (PC)
The program counter is a 16-bit counter that indicates the memory address of the instruction
currently being executed by the CPU. Instruction execution, interrupts, resets, and similar
update the contents of the program counter. The initial value during a reset is the read address
of the mode data (FFFD
Accumulator (A)
The accumulator is a 16-bit arithmetic operation register. The accumulator is used to perform
arithmetic operations and data transfers with data in memory or in other registers such as the
temporary accumulator (T). The content of the accumulator can be treated as either word (16-
bit) or byte (8-bit) data. Only the lower 8 bits (AL) of the accumulator are used for byte arithmetic
operations or transfers. In this case, the upper 8 bits (AH) remain unchanged. The initial value
32

Figure 3.2-1 Dedicated Register Configuration

16 bits
: Program counter
PC
: Accumulator
A
T
: Temporary accumulator
IX
: Index register
EP
: Extra pointer
SP
:Stack pointer
: Program status
RP CCR
PS
).
H
A register for indicating the current instruction
storage positions
A temporary register for storing arithmetic operations or
transfer instructions
A register which performs arithmetic operations with the
accumulator
A register for indicating an index address
A pointer for indicating a memory address
A register for indicating the current stack location
A register for storing a register bank pointer and
condition code