hi,

as we know tmod register is used for timer or counter mode control. tmod is the 8bit register in which,lower 4 bit is used for timer/counter 0 & higher 4 bit is used for timer/counter 1,
open ur reference book,see the bits of tmod.ok now i m coming to ur problem.(always remember tmod is byte addressable register,we cant configure bit wise,we have to configure byte wise)

mov tmod,#02h
here 'h' is representing its a hexa decimal number so when it will be store in tmod the configuration will be 0000 0010,so timer 0 mode 2 will be selected.

mov tmod,#11010101b

gate c/bar(t) m1 m0 | gate c/bar(t) m1 mo
|
1 1 0 1 | 0 1 0 1

higher 4 bitS is telling....
its a counter 1 in mode 1 ,& THE COUNTER WILL RUN WHEN

TR1 BIT -'HIGH' AND EXTERNAL INTERRUPT 'INT1'--'HIGH'.SO BOTH MUST BE HIGH TO START THE COUNTER.

LOWER 4 BITS IS TELLING....
COUNETR 0 IN MODE 1,AND IT WILL START WHEN ONLY TR0 BIT WILL BE 'HIGH',
the combination of counter and timer which can be selected by tmod,c- counter,t- timer
c|c
c|t
t|c
t|t

hope u got it