D17133CS datasheet(35/289 Pages) NEC

35 / 289 page

CHAPTER 3

PROGRAM COUNTER (PC)

Figure 3-2. Value of the Program Counter after an Instruction Is Executed

Program Counter Bit

Program Counter Value

Instruction

PC9 PC8 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0

During reset

BR addr

CALL addr

BR @AR

CALL @AR

Value in the address register (AR)

(MOVT DBF, @AR)

RET

RETSK

RETI

During interrupt

Each interrupted vector address

3.2.1 Program Counter at Reset

By setting the RESET terminals to low, the program counter is set to 000H.

Figure 3-3. Value in the Program Counter after Reset

Value set by addr

Value in the address stack register location pointed to the

stack pointer (return address)

MSB

All bits are set to 0

000000000

LSB

3.2.2 Program Counter during Execution of the Branch Instruction (BR)

There are two ways to specify branching using the branch instruction. One is to specify the branch address in

the operand using the direct branch instruction (BR addr). The other is to branch to the address specified by the

address register using the indirect branch instruction (BR @AR).

The address specified by a direct branch instruction is placed in the program counter.

Figure 3-4. Value in the Program Counter during Execution of a Direct Branch Instruction

MSB

PC9

PC8

PC7

PC6

PC5

PC4

PC3

PC2

PC1

PC0

LSB

Address specified by addr

An indirect branch instruction causes the address in the address counter to be placed in the program counter.

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