The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

20-18

THE

x86 MICROPROCESSORS

Example 20.9

ORG 0

MOV TMOD,#02H ;timer 0 in mode 2

MOV TH0,#0H ;TH0 = 0

SETB TR0 ;start the timer

CHECK: JNB TF0,CHECK ;loop to CHECK if TF0 = 0

CLR TF0 ;clear TF0

CPL P1.3 ;complement P1.3

SJMP CHECK ;jump to CHECK

END

The program in Example 20.9 generates a square wave on pin P1.3. It uses Timer 0 in

mode 2. The count loaded in TH0 is 0. Note that, after TF0 is cleared, there is no ‘re-

load’ operation for TH0. The count is automatically re-loaded by the 8051, after the

timer flag is cleared.

Now let us calculate the frequency of the square wave, generated (assuming an 8051

with a clock frequency of 1MHz). ...