8051 ASSEMBLY 
                  LANGUAGE 
               PROGRAMMING
          The 8051 Microcontroller and Embedded 
          Systems: Using Assembly and C
          Mazidi, Mazidi and McKinlay
                       Chung-Ping Young
                                  楊中平
      Home Automation, Networking, and Entertainment Lab
      Dept. of Computer Science and Information Engineering 
      National Cheng Kung University, TAIWAN
         INSIDE THE     ‰ Register are used to store information 
            8051           temporarily, while the information 
                           could be 
          Registers         ¾ a byte of data to be processed, or 
                            ¾ an address pointing to the data to be 
                              fetched
                        ‰ The vast majority of 8051 register are 
                           8-bit registers
                            ¾ There is only one data type, 8 bits
               HANEL    Department of Computer Science and Information Engineering
                        National Cheng Kung University, TAIWAN           2
             INSIDE THE               ‰ The 8 bits of a register are shown from 
                   8051                   MSB D7 to the LSB D0
                                           ¾ With an 8-bit data type, any data larger 
                Registers                      than 8 bits must be broken into 8-bit 
                   (cont’)                     chunks before it is processed
                                                                most                   least 
                                                           significant bit        significant bit
                                               D7       D6      D5       D4      D3      D2       D1      D0
                                                                     8 bit Registers
                       HANEL         Department of Computer Science and Information Engineering
                                     National Cheng Kung University, TAIWAN                                        3
         INSIDE THE      ‰ The most widely used registers 
            8051            ¾ A (Accumulator)
                                ƒ For all arithmetic and logic instructions
          Registers         ¾ B, R0, R1, R2, R3, R4, R5, R6, R7 
            (cont’)         ¾ DPTR (data pointer), and PC (program 
                              counter)
                                  A
                                  B
                                  R0           DPTR     DPH        DPL
                                  R1
                                  R2            PC     PC (Program counter)
                                  R3
                                  R4
                                  R5
                                  R6
                                  R7
               HANEL    Department of Computer Science and Information Engineering
                        National Cheng Kung University, TAIWAN            4