What is procedure for calculating time delay(TH0&TL0)
The operation of the timers is described in the so-called "bible" for the 8051: Chapter 1 - 80C51 Family Architecture: http://www.semiconductors.philips.com/acrobat/various/80C51_FAM_ARCH_1.pdf Chapter 2 - 80C51 Family Programmer's Guide and Instruction Set: http://www.semiconductors.philips.com/acrobat/various/80C51_FAM_PROG_GUIDE_1.pdf Chapter 3 - 80C51 Family Hardware Description: http://www.semiconductors.philips.com/acrobat/various/80C51_FAM_HARDWARE_1.pdf The description of the Timers starts on p6 of Chapter 3, but you would do well to download all three documents and keep them close to hand for reference!