EM78P153EP Ver la hoja de datos (PDF) - ELAN Microelectronics

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EM78P153EP

8-bit microprocessor designed and developed with low-power and high-speed CMOS technology

ELAN Microelectronics 

EM78P153E

OTP ROM

3. R2 (Program Counter) & Stack

• Depending on the device type, R2 and hardware stack are 9-bit wide. The structure is depicted in

Fig.3.

• 512×13 bits on-chip OTP ROM addresses to the relative programming instruction codes. One

program page is 512 words long.

• R2 is set as all "0"s when under RESET condition.

• "JMP" instruction allows direct loading of the lower 9 program counter bits. Thus, "JMP" allows PC to

go to any location within a page.

• "CALL" instruction loads the lower 9 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-level

stack.

• "ADD R2,A" allows the contents of ‘A’ to be added to the current PC, and the ninth 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 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 bits (A8) of the PC to be cleared. Thus, the computed jump is limited to the first 256 locations

of a page.

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

change the contents of R2. This instruction will need one more instruction cycle.

PC

00

A8

A7 ~ A0

00

000 Page 0

1FF

CALL

RET

RETL

RETL K

Stack 1

Stack 2

Stack 3

Stack 4

Stack 5

Fig. 3 Program Counter Organization

This specification is subject to change without prior notice.

7

2002/03/01

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