3

I/O PORTS AND SPECIAL FUNCTION REGISTERS

CHAPTER OBJECTIVES

In this chapter, the reader is introduced to some Special Function Registers (SFRs) and the overall architecture of the I/O ports of MCS-51. After completion of the chapter, the reader should be able to understand

  • Names, locations (addresses), reset values and functions of all SFRs.
  • Details of PSW, accumulator, B register, SP and I/O port registers.
  • How to select any one of the four register banks of MCS-51.
  • Bit addresses of different SFRs.
  • Architecture and functioning of all four I/O ports of MCS-51.
  • Difference between MCS-51 I/O ports and 8255 I/O ports.

3.1 | Introduction

In Chapter 2, it was mentioned that some of the internal memory locations (80H to FFH) of MCS-51 contain SFRs. ...

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