IBM EM78P312N manual Bit Microcontroller R0 Indirect Addressing Register, R1 Time Clock /Counter

EM78P312N

8-Bit Microcontroller

R0 (Indirect Addressing Register)

R0 is not a physically implemented register. Its major function is to act as an indirect addressing pointer. Any instruction using R0 as a pointer actually accesses data pointed by the RAM Select Register (R4).

R1 (Time Clock /Counter)

This register is writable and readable just like the other registers. The contents of the prescaler counter are cleared only when a value is written into the TCC register.

R2 (Program Counter) & Stack

zDepending on the device type, R2 and hardware stack are 10-bit wide. The structure is depicted in Fig.5-3.

zGenerates 8192 ⋅13 bits on-chip OTP ROM addresses to the relative programming instruction codes. One program page is 1024 words long.

zR2 is set as all "0"s when under RESET condition

z"JMP" instruction allows direct loading of the lower 10 program counter bits. Thus, "JMP" allows the PC to go to any location within a page.

z"CALL" instruction loads the lower 10 bits of the PC, and then PC+1 is pushed onto the stack. Thus, the subroutine entry address can be located anywhere within a page.

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

zAll instructions are single instruction cycle (fclk/2 or fclk/4) except for the instruction that would change the contents of R2. Such instruction will need one more instruction cycle.

zFor an interrupt trigger, the program ROM will jump to individual interrupt vector at Page 0. The CPU will store ACC, R3 status and R5 PAGE automatically, it will restore after instruction RETI.

Product Specification (V1.0) 10.03.2006 • 5

(This specification is subject to change without further notice)