EM78451AP EMC [ELAN Microelectronics Corp], EM78451AP Datasheet - Page 8

• Manufacturer Part Number: EM78451AP
• Description: 8-Bit Microcontroller
• Manufacturer: EMC [ELAN Microelectronics Corp]

EM78451
8-Bit Microcontroller
4 •
4.1 Operational Registers
4.1.1 R0 (Indirect Address Register)
R0 is not a physically implemented register. It is used as an indirect addressing
pointer. Any instruction using R0 as register actually accesses data pointed by the
RAM Select Register (R4).
4.1.2 R1 (TCC)
4.1.3 R2 (Program Counter) & Stack
It is increased by the instruction cycle clock.
Written and read by program as any other register.
R2 and the hardware stacks are 12 bits wide.
The structure is depicted in Fig. 3.
Generates 4K × 13 on-chip ROM addresses to the relative programming instruction
All the R2 bits are set to "1"s as RESET condition occurs.
"JMP" instruction allows direct loading of the lower 10 program counter bits. Thus,
"JMP" allows it to jump to any location on one page.
"CALL" instruction loads the lower 10 bits of the PC, and then PC+1 is pushed into
"RET" ("RETL k", "RETI") instruction loads the program counter with the contents
"MOV R2, A" allows the loading of an address from the "A" register to the lower 8
"ADD R2, A" allows a relative address to be added to the current PC, and the ninth
Any instruction that is written to R2 (e.g. "ADD R2, A", "MOV R2, A", "BC R2,6",⋅⋅⋅⋅⋅)
"TBL" allows a relative address to be added to the current PC (R2+A→R2), and
codes. One program page is 1024 words long.
the stack. Thus, the subroutine entry address can be located anywhere within a
page.
at the top of stack.
bits of PC, and the ninth and tenth bits (A8~A9) of PC are cleared.
and tenth bits of PC are cleared.
(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.
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) 256th locations on one
program page.
(This specification is subject to change without further notice)
Product Specification (V1.2) 05.27.2004