Timing calculation method of single chip microcomputer timer

For 12MHz, 1 machine cycle is 1us, 12/fosc = 1us.

Mode 0: 13-bit timer maximum time interval = 2^13 = 8.192ms.
Mode 1: 16-bit timer maximum time interval = 2^16 = 65.536ms.
Mode 2: 8-bit timer maximum time interval = 2^8 = 0.256ms. =256 us.

Timing is 5ms. Calculate the initial value of the timer M = 2^KX*Fosc/12. 12MHz
mode 0: K=13,X=5ms,Fosc=12MHz. Then M = 2^13 - 5*10^(-3)*12*10^6/12= 3192 = 0x0C78. 
       THx = 0CH,TLx = 78H,
   mode 1: K=16,X=5ms,Fosc=12MHz. Then M = 2^16 - 5*10^(-3)*12*10^6/12= 60536 = 0xEC78
       THx = ECH,TLx = 78H,  

     50ms 12MHz THx = 3CH,TLx = B0H, 
       10ms THx = D8H,TLx = F0H,  
 Method 2: Maximum time 2^8Fosc/12 = 0.256ms

  Where does the decimal number come from?
  6MHz One machine cycle 12/6 = 2us
  Timing 1ms Counting initial value x
 (2^16-x)*2us = 1000us
 x = 2^16 - 500, TH, TL can be set to -500
 
12MHz One machine cycle 12/12 = 1us
12MHz One machine cycle 12/12 = 1us
 Timing 50ms Counting initial value x
 (2^16-x)*1us = 50000us
 x = 2^16 - 50000, TH, TL can be set to -500

Timer Counts the internal crystal frequency
Counter Counts the number of pulses on the external input CPU pin P3.4 (T0) P3.5 (T1) Negative jump plus one
When the crystal oscillator is 6MHz, the maximum counting frequency is 500KHz

Register 
1 TH TL
2 TCON
  TR0 TR1 Other bits are interrupt control bits

TMOD
GATE C/T1 M1 M0 GATE C/T0 M1 M0


C8051F00X
timer: add 1 for each clock. The clock can be the system clock or 1/12 of the system clock. When a level appears on the
CKCON  

pin, start T0. When it is not satisfied, stop T0 and clear it after reading.