em78f644nso28s ELAN Microelectronics Corp, em78f644nso28s Datasheet - Page 23

• Manufacturer Part Number: em78f644nso28s
• Description: Flash Series 8-bit Microcontroller
• Manufacturer: ELAN Microelectronics Corp

6
Product Specification (V1.0) 05.05.2010
(This specification is subject to change without further notice)
Functional Description
6.1 Operational Registers for EM78F64xN/54xN
6.1.1 R0 (Indirect Addressing Register)
R0 is not a physically implemented register. It is used as an indirect addressing
pointer. Any instruction that uses 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 the 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 content of
the prescaler counter is cleared only when the TCC register is written with a value.
6.1.3 R2 (Program Counter and Stack)
Depending on the device type, R2 and hardware stack are 12-bit wide. The
structure is depicted in Figure 6-1a below.
The configuration structure generates 4K×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 the 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
onto the stack. Thus, the subroutine entry address can be located anywhere
within a page.
"LJMP" instruction allows direct loading of the program counter bits (A0~A11).
Therefore, "LJMP" allows the PC to jump to any location within 4K (2
"LCALL" instruction loads the program counter bits (A0 ~A11), and then PC+1 is
pushed onto the stack. Thus, the subroutine entry address can be located
anywhere within 4K (2
"RET" ("RETL k", "RETI") instruction loads the program counter with the contents
of the top-level stack.
12
)
EM78F648/644/642/641/548/544/542/541N
8-Bit Microcontroller
12
).
• 13