EM78F651NAPSSLASHNAPJ datasheet(10/58 Pages) EMC

10 / 58 page

EM78F651N

8-Bit Microcontroller

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Product Specification (V1.1) 10.20.2006

(This specification is subject to change without further notice)

Function Description

6.1 Operational Registers

6.1.1 R0 (Indirect Addressing Register)

R0 is not a physically implemented register. It is used as an indirect addressing

pointer. Any instruction using R0 as a pointer actually accesses data pointed by the

RAM Select Register (R4).

6.1.2 R1 (Timer Clock/Counter)

R1 is incremented by an external signal edge, which is defined by TE bit (CONT-4)

through the TCC pin, or by the instruction cycle clock. It is writable and readable as

any other registers. It is defined by resetting PSTE (CONT-3).

The prescaler is assigned to TCC, if the PSTE bit (CONT-3) is reset. The contents of

the prescaler counter are cleared only when the TCC register is written with a value.

6.1.3 R2 (Program Counter) & Stack

Depending on the device type, R2 and hardware stack are 10-bit wide. The structure

is depicted in Fig 6-1.

The configuration structure generates 1024

×13 bits on-chip Flash ROM addresses to

the relative programming instruction codes. One program page is 1024 words long.

R2 is set as all "0"s when under a reset condition.

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

"JMP" allows PC to go 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-level stack.

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

and above bits of the PC will increase progressively.

"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 won’t be changed.

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

etc.) will cause the ninth bit and the tenth bit (A8~A9) of the PC to remain unchanged.

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