EM78P451S
8-Bit Microcontroller with OTP ROM
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"JMP" instruction allows direct loading of the lower 10 program counter bits. Thus,
"JMP" allows jump to any location on one 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
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"RET" ("RETL k", "RETI") instruction loads the program counter with the contents
at the top of stack.
"MOV R2, A" allows the loading of an address from the "A" register to the lower 8
bits of PC, and the ninth and tenth bits (A8~A9) of PC are cleared.
"ADD R2, A" allows a relative address be added to the current PC, and the ninth
and tenth bits of PC are cleared.
Any instruction that is written to R2 (e.g. "ADD R2, A", "MOV R2, A", "BC R2,6",⋅⋅⋅⋅⋅)
(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.
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"TBL" allows a relative address be added to the current PC (R2+A→R2), and
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) 256 locations on one program
page.
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In case of EM78P451S, the most significant bits (A10~A11) will be loaded with the
contents of bits PS0~PS1 in the status register (R3) upon the execution of a "JMP",
"CALL", or any other instructions which writes to R2.
All instructions are single instruction cycle (fclk/2 or fclk/4) except for the instruction
that would change the contents R2. Such instruction will need one more
instruction cycle.
R3
000H
001H
002H
A11 A10 A9 A8
A7
~
A0
Hardware Vector
Software Vector
CALL
RET
RETL
On-chip Program
Memory
RETI
00 PAGE0 0000~03FF
Stack Level 1
Stack Level 2
Stack Level 3
Stack Level 4
Stack Level 5
01 PAGE1 0400~07FF
10 PAGE2 0800~0BFF
11 PAGE3 0C00~0FFF
Reset Vector
FFFH
Fig. 3 Program Counter Organization
Product Specification (V1.0) 06.01.2004
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(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
