EM78459AM datasheet(12/62 Pages) EMC

12 / 62 page

EM78458/459

8-Bit Microcontroller with MASK ROM

•

Product Specification (V1.4) 05.27.2005

(This specification is subject to change without further notice)

"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 EM78458/459, 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 ~ A8

A 11~A 10

A 7

A 0

Page 0

Page 1

Page 2

Page 3

000

3FF

400

7FF

BFF

FFF

C00

800

CALL K

RET

RETI

RETL K

Stack 0

Stack 1

Stack 2

Stack 3

Stack 4

Stack 5

Stack 6

Stack 7

Fig. 3 Program Counter Organization

EM78459AM Datasheet(PDF) 12 Page - ELAN Microelectronics Corp

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