INTRODUCTION TO MICROCONTROLLERS(8051) ARCHITECTURE,INSTRUCTION SET ,ADDRESSING MODES

Meeting the computing needs of the task at hand efficiently and cost effectively Speed Packaging Power consumption The amount of RAM and ROM on chip The number of I/O pins and the timer on chip How easy to upgrade to higher performance or lower power-consumption versions Cost per unitIntel introduced 8051, referred as MCS- 51, in 1981. The 8051 is an 8-bit processor The CPU can work on only 8 bits of data at a time The 8051 became widely popular after allowing other manufactures to make and market any flavor of the 8051. 64KB Program Memory address space 64KB Data Memory address space 4K bytes of on-chip Program Memory 128 bytes of on-chip Data RAM 32 bidirectional and individually addressable I/0 lines Two 16-bit timer/counters Full duplex UART 6-source/5-vector interrupt structure with two priority levels On-chip clock oscillator There are 128 bytes of RAM in the 8051. Assigned addresses 00 to 7FH The 128 bytes are divided into 3 different groups as follows: A total of 32 bytes from locations 00 to 1F hex are set aside for register banks and the stack. A total of 16 bytes from locations 20H to 2FH are set aside for bit-addressable read/write memory. A total of 80 bytes from locations 30H to 7FH are used for read and write storage, called scratch pad. The stack is a section of RAM used by the CPU to store information temporarily. This information could be data or an address The register used to access the stack is called the SP (stack pointer) register The stack pointer in the 8051 is only 8 bit wide, which means that it can take value of 00 to FFH When the 8051 is powered up, the SP register contains value 07 RAM location 08 is the first location begin used for the stack by the 8051 The storing of a CPU register in the stack is called a PUSH SP is pointing to the last used location of the stack As we push data onto the stack, the SP is incremented by one This is different from many microprocessors Loading the contents of the stack back into a CPU register is called a POP With every pop, the top byte of the stack is copied to the register specified by the instruction and the stack pointer is decremented once The CPU can access data in various ways, which are called addressing modes Immediate Register Direct Register indirect External D These instructions perform several basic operations. After execution, the result is stored in the first operand. 8 bit addition, subtraction, multiplication, increment-decrement instructions can be performed. MNEMONICS DESCRIPTION BYTE ADD A, Rn A = A + Rn 1 ADD A, @ Ri A = A+ Ri 1 ADD A, # X A = A + Byte 2 ADDC A, Rn A = A + Rn + C 1 LCALL (long call): 3-byte instruction 2-byte address Target address within 64K-byte range ACALL (absolute call): 2-byte instruction 11-bit address Target address within 2K-byte range All conditional jumps are short jumps Target address within -128 to +127 of PC LJ