EM78P458AM datasheet(9/76 Pages) EMC

9 / 76 page

EM78P458/459

OTP ROM

• "JMP" instruction allows the direct loading of the lower 10 program counter bits. Thus, "JMP" allows

PC to jump to any location within a page.

• "CALL" instruction loads the lower 10 bits of the PC, and then PC+1 is pushed into the stack. Thus,

the subroutine entry address can be located anywhere within a page.

• "RET" ("RETL k", "RETI") instruction loads the program counter with the contents of the top of stack.

• "ADD R2, A" allows a relative address to be added to the current PC, and the ninth and tenth bits of

the PC are cleared.

• "MOV R2, A" allows to load an address from the "A" register to the lower 8 bits of the PC, and the

ninth and tenth bits of the PC are cleared.

• Any instruction that is written to R2 (e.g. "ADD R2, A", "MOV R2, A", "BC R2, 6",

⋅⋅⋅⋅⋅) will cause the

ninth bit and the tenth bit (A8~A9) of the PC to be cleared. Thus, the computed jump is limited to the

first 256 locations of a page.

• In the case of EM78P458/459, the most two significant bits (A11 and A10) will be loaded with the

content of PS1 and PS0 in the status register (R3) upon the execution of a "JMP", "CALL", or any

other instructions set which write to R2.

• All instructions are single instruction cycle (fclk/2 or fclk/4) except for the instructions which write to

R2, need one more instruction cycle.

A9 ~ A0

Stack Level 0

Stack Level 2

Stack Level 1

Stack Level 3

Stack Level 4

000H

FFFH

008H

Interrupt Vector

Reset Vector

A11, A10

On-chip Program Memory

Page 0

Page 1

Page 2

Page 3

Stack Level 5

Stack Level 6

Stack Level 7

0 0 0

3 F F

4 0 0

7 F F

8 0 0

B F F

C 0 0

F F F

Fig. 3 Program Counter Organization

This specification is subject to change without prior notice.

06.25.2004 (V1.4)

EM78P458AM Datasheet(PDF) 9 Page - ELAN Microelectronics Corp

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