TSC80251 TEMIC [TEMIC Semiconductors], TSC80251 Datasheet - Page 23

• Manufacturer Part Number: TSC80251
• Manufacturer: TEMIC [TEMIC Semiconductors]

TSC80251
3.4.2.1. Accumulator and B Register
The 8–bit accumulator (A) is byte register R11, which is also accessible in the SFR space as A at S:0E0h (See
Figure 3.7. ). The B register, used in multiplies and divides, is register R10, which is also accessible in the SFR space
as B at S:0F0h. Accessing A or B as a register is one state faster than accessing them as SFRs.
Instructions in the C51 Architecture use the accumulator as the primary register for data moves and calculations.
however, in the C251 Architecture, any of registers R1-R15 can serve for these tasks. As a result, the accumulator does
not play the central role that it has in 80C51 microcontrollers.
3.4.2.2. Extended Data Pointer, DPX
Dword register DR56 is the extended data pointer, DPX (See Figure 3.7. ). The lower three bytes of DPX (DPL, DPH
and DPXL) are accessible as SFRs. DPL and DPH comprise the 16–bit data pointer DPTR. While instructions in the
C51 Architecture always use DPTR as the data pointer, instructions in the C251 Architecture can use any word or dword
register as a data pointer.
DPXL, the byte in location 57, specifies the region of memory (00:-FF:) that maps into the 64–Kbyte external data
memory space in the C51 Architecture. In other words, the MOVX instruction addresses the region specified by DPXL
when it moves data to and from external memory. The reset value of DPXL is 01h.
3.4.2.3. Extended Stack Pointer, SPX
Dword register DR60 is the stack pointer, SPX (See Figure 3.7. ). The byte at (location 63) is the 8–bit stack pointer,
SP, in the C51 Architecture. The byte at location 62 is the stack pointer high, SPH. The two bytes allow the stack to
extend to the top of memory region 00:. SP and SPH can be accessed as SFRs.
Two instructions, PUSH and POP directly address the stack pointer. Subroutine calls (ACALL, ECALL, LCALL) and
returns (ERET, RET, RETI) also use the stack pointer. To preserve the stack, do not use DR60 as a general–purpose
register.
Rev. C – May 7, 1999
3.7