UPD17P136ACT datasheet(44/292 Pages) NEC

44 / 292 page

CHAPTER 4 PROGRAM MEMORY (ROM)

(2) Direct branch

A direct branch (BR addr) instruction branches a value of operand (addr) as an address. (In the case of the

µPD17134A and µPD17135A, the most significant bit must be 0. If an address is specified outside of this range,

an error will occur in the assembler.) A BR addr instruction can be used to branch to any address in program

memory.

(3) Indirect branch

When executing an indirect branch (BR @AR), the program branches to the address specified by the value

stored in the address register (AR). A BR @AR can be used to branch to any address in program memory.

Also see 7.2 ADDRESS REGISTER (AR).

(4) Subroutine

To branch execution to a subroutine, the subroutine call (CALL) instruction is used.

The CALL instruction can be used in two ways: as a direct subroutine call instruction (CALL addr) that causes

execution to branch using the value of the operand (addr) as an address, and as an indirect subroutine call

instruction (CALL @AR) that causes execution to branch using the contents of an address register as an

address.

To return from a subroutine, the RET or RETSK instruction is used. By executing the RET or RETSK instruction,

execution is returned to the program memory address next to the one at which the CALL instruction was

executed.

When the RETSK instruction is used, the first instruction after execution has returned from the subroutine is

executed as a NOP instruction.

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