Balakumar AP/ECE

DEPARTMENT OF MECHATRONICS ENGINEERING MT6601 – MICROCONTROLLER AND PLC IMPORTANT QUESTIONS PART A      List some special function register of 8051.                What are the flags supported by 8051 controller? State the function of RS1 and RS0 bits in the flag register of 8051. 4.       How we can change level and edge triggering characteristics of 8051 external interrupts? 5.       How baud rate will be calculated in mode1 and mode   6.       Define  two-key Roll over.              7.        What is latch? Where it is used?              8.        What do you mean by ladder logic?               9.       List down the types of buses ...

This has to do with the arrangement used to generate baud rate frequency. There is only an 8 bit timer/counter (T1) available for generating the baud rate clock. It is used in mode 2 (auto reload). To get good computational speed, the crystal has to have a high frequency. The propagation delays of the datapaths allow around 12 MHz. If we try to divide the crystal frequency directly, then to get the lowest baud rate of 300, we would need a divisor of 12*10^6/300 = 40000. It would have not been possible with an 8 bit counter. Therefore the crystal frequency is first divided by 12 and then by 32 before giving it to the counter. Now the counter could manage baud rates as low as 12*10^6/256/12/32 = 122. But if we use a round figure frequency of 12 MHz for the crystal, then the division factors turn out to be fractional. For 300 baud we need a divisor of 104.1. Choosing the nearest integer 104 does not matter much here but the situation is much worse for high baud rates. For 9...