Write the difference between LDA and STA instruction ?
LDA : Load data in to Accumulator register(A) directly from the address specified with in the instruction.
STA : Store the contents of Accumulator register(A) to the address specified with in the instruction.
What are the types of rotate instructions ?
RLC : Rotate Accumulator Left
RRC : Rotate Accumulator Right
RAL : Rotate Accumulator Left through Carry
RAR : Rotate Accumulator Right through Carry
What are the operating modes of 8255 ?
Bit set/Reset mode
mode 0 : Simple input/output
mode 1 : Input/output with handshake
mode 2 : Bi-directional I/O data transfer
What are the priority modes in 8259 ?
Fully nested mode
Special fully nested mode
Rotating priority mode
Special mask mode
What is the use of SWAP function in 8051 ?
SWAP A : Swap nibbles with in the Accumulator bytes.
It interchanges the low and high order nibbles of the Accumulator (bits 0-3 and bits 4-7)
What is SCON ?
SCON is the serial port control register , which contains not only the mode selection bits
(SM0 : SM2 ,REN), but also the 9th data bit for transmit and receive (TB8 and RB8) and the serial port interrupt bits (TI and RI).
SM0 : Serial port mode control bit 0
SM1 : Serial port mode control bit 1
SM2 : Serial port mode control bit 2
REN : Receiver enable control bit
TB8 : Transmit bit 8
RB8 : Receive bit 8
TI : Transmit Interrupt flag
RI : Receive interrupt flag
How we calculate the Baud rate for serial port in mode 0 ?
Baud Rate = Oscillator frequency/12
What is the significance of TXD and RXD pins in 8051 ?
TXD : Transmit data pin for serial port in UART mode. Clock output in shift register mode.
RXD : Receive data pin for serial port in UART mode. Data I/O pin in shift register mode.
Write two examples of Register indirect Addressing modes in 8051 ?
MOV A,@R0 ; Load thecontents pointed by R0 in A.
ADD A,@R1 ; Add thecontents of A and thecontents pointed by R1.
What is Accumulator Register ?
It is an 8 : bit register. It holds a source operand and receives the result of the arithmetic instructions (Addition, Subtraction, Multiplication and Division)