EM78P451SWM datasheet(9/54 Pages) EMC

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EM78P451S

8-Bit Microcontroller with OTP ROM

Product Specification (V1.0) 06.01.2004

• 5

(This specification is subject to change without further notice)

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

"JMP" allows jump to any location on one 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

at the top of stack.

"MOV R2, A" allows the loading of an address from the "A" register to the lower 8

bits of PC, and the ninth and tenth bits (A8~A9) of PC are cleared.

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

and tenth bits of PC are cleared.

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

⋅⋅⋅⋅⋅)

(except "TBL") will cause the ninth and tenth bits (A8~A9) of PC to be cleared.

Thus, the computed jump is limited to the first 256 locations of any program page.

"TBL" allows a relative address be added to the current PC (R2+A

→R2), and

contents of the ninth and tenth bits (A8~A9) of PC are not changed. Thus, the

computed jump can be on the second (or third, 4th) 256 locations on one program

page.

In case of EM78P451S, the most significant bits (A10~A11) will be loaded with the

contents of bits PS0~PS1 in the status register (R3) upon the execution of a "JMP",

"CALL", or any other instructions which writes to R2.

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

that would change the contents R2. Such instruction will need one more

instruction cycle.

On-chip Program

Memory

000H

FFFH

001H

Hardware Vector

Software Vector

Reset Vector

002H

A9 A8

A11 A10

Stack Level 1

Stack Level 3

Stack Level 2

Stack Level 4

Stack Level 5

CALL

00 PAGE0 0000~03FF

01 PAGE1 0400~07FF

10 PAGE2 0800~0BFF

11 PAGE3 0C00~0FFF

RET

RETL

RETI

Fig. 3 Program Counter Organization

EM78P451SWM Datasheet(PDF) 9 Page - ELAN Microelectronics Corp

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