Dedicated Registers - Fujitsu F2MC-8FX Hardware Manual

CHAPTER 5 CPU
5.1

Dedicated Registers

The CPU has its dedicated registers: the program counter (PC), two arithmetic registers
(A and T), three address pointers (IX, EP, and SP), and the program status (PS) register.
Each of the registers is 16 bits long. The PS register consists of the register bank
pointer (RP), direct pointer (DP), and condition code register (CCR).
Configuration of Dedicated Registers
The dedicated registers in the CPU are seven 16-bit registers. Accumulator (A) and temporary accumulator
(T) can also be used with only their lower eight bits in service.
Figure 5.1-1 shows the configuration of the dedicated registers.
Address
FFFD
H
0000
H
0000
H
0000
H
0000
H
0000
H
0030
H
Functions of Dedicated Registers
Program counter (PC)
The program counter is a 16-bit counter which contains the memory address of the instruction currently
executed by the CPU. The program counter is updated whenever an instruction is executed or an interrupt
or reset occurs. The initial value set immediately after a reset is the mode data read address (FFFD
Accumulator (A)
The accumulator is a 16-bit register for arithmetic operation. It is used for a variety of arithmetic and
transfer operations of data in memory or data in other registers such as the temporary accumulator (T). The
data in the accumulator can be handled either as word (16-bit) data or byte (8-bit) data. For byte-length
arithmetic and transfer operations, only the lower eight bits (AL) of the accumulator are used with the
upper eight bits (AH) left unchanged. The initial value set immediately after a reset is 0000
32
Figure 5.1-1 Configuration of Dedicated Registers
16 bits
PC
AH AL
TH TL
IX
EP
SP
DP CCR
RP
PS
: Program counter
Contains the address of the current instruction.
: Accumulator (A)
Temporary storage register for arithmetic operation and
transfer.
: Temporary accumulator (T)
Performs an operation with accumulator.
: Index register
Register containing an index address.
: Extra pointer
Pointer containing a memory address.
: Stack pointer
Contains the current stack location.
: Program status
Register consisting of the register bank pointer, direct bank
pointer, and condition code register.
).
H
.
H