8051 Microcontroller

Program Status Register PSW of 8051 The 8051 has a 8-bit PSW register which is alsoknown as Flag register.In the 8-bit register only 6-bits are used by 8051.The two unused bits are user definable bits.In the 6-bits four of them are conditional flags .They are Carry –CY,Auxiliary Carry-AC, Parity-P,and Overflow-OV .These flag bits indicate some conditions that resulted after an instruction was executed. The bits PSW3 and  PSW4  are  denoted as RS0 and RS1 and these bits are used th select the bank registers of the RAM location. The meaning of various bits of PSW register is shown below. CY                              PSW.7                       Carry Flag AC                              PSW.6                       Auxiliary Carry Flag FO                              PSW.5                        Flag 0 available for general purpose . RS1                            PSW.4                        Register Bank select bit 1 RS0                            PSW.3             

The 8051 microcontroller is a very popular 8-bit microcontroller introduced by Intel in the year 1981 and it has become almost the academic standard now a days.  The 8051 is based on an 8-bit CISC core with Harvard architecture. Its 8-bit architecture is optimized for control applications with extensive Boolean processing. It is available as a 40-pin DIP chip and works at +5 Volts DC. The salient features of 8051 controller are given below. salient features of 8051 SALIANT FEATURES: The salient features of 8051 Microcontroller are  i. 4 KB on chip program memory (ROM or EPROM)). ii. 128 bytes on chip data memory(RAM). iii. 8-bit data bus iv. 16-bit address bus v. 32 general purpose registers each of 8 bits vi. Two -16 bit timers  T0 and T1 vii. Five Interrupts (3 internal and 2 external). ix. Four  Parallel ports each of 8-bits (PORT0, PORT1,PORT2,PORT3) with a total of 32 I/O     lines. x. One 16-bit program counter and One 16-bit DPTR ( data pointer) xi. One 8-bi

SPECIAL FUNCTION REGISTERS (SFRs) of 8051 In 8051 microcontroller there certain registers which uses the RAM addresses from 80h to FFh and they are meant for certain specific operations .These registers are called Special function  registers (SFRs).Some of these registers are bit addressable also. The list of SFRs and their functional names are given below. In these SFRs some of them are related to  I/O ports (P0,P1,P2 and P3) and some of them are meant for control operations (TCON,SCON, PCON..) and remaining are  the auxillary SFRs, in the sense that they don't directly configure the 8051. The following table shows the layout of each record in 8051 and 8052 microcontroller. F8H FFH F0H B *  F7H E8H EFH E0h ACC *  E7H D8H DFH D0H PSW *  D7H C8H T2CON * #  RCAP2L #  RCAP2H #  TL2 #  TH2 #  CFH C0h C7H B8H IP *  BFH B0h P3 *  B7H A8h IE *  AFH A0H P2 *  A7H 98H SCON *  SBUF 9FH 90H P1 *  97H 88h TCON *  TMOD TL0 TL1 TH0 TH1 8FH 80H P0 *  SP DPL DPH PCON 87H