Four working modes and functions of T0 and T1 of mcs-51 single chip microcomputer and calculation of timing initial value

1. Mode 0
When bit M1M0=00. T is a 13-bit counter, THi is the high 8 bits, and TLi is the low 5 bits. 

The design value is N, then the initial value of the count is X=2^13-N; 2^13=8192=2000H 

Example 1: Assume fosc=6MHz, and use T1 mode 0 for 10ms. Find the initial values ​​of TH1 and TL1. 

The design initial value is X; from the known conditions: 1 machine cycle=12/fosc=2us; 

10,000us=12/fosc*(2^13-X)us 

X=2^13-10000/2=8192-5000=3192=0C78H 

So: TL1=18H, TH1=63H 

2. Mode 1 

When bit M1M0=01. T is a 16-bit counter, THi is the high 8 bits, and TLi is the low 8 bits. 

If the design value is N, then the initial value of the count is X=2^16-N; 2^16==65536=10000H 

Example 2: Assume fosc=6MHz, and use T1 mode 1 for 100ms. Find the initial values ​​of TH1 and TL1. 

The initial value of the design number is X; from the known conditions, we get: 1 machine cycle=12/fosc=2us; 

100,000us=12/fosc*(2^16-X)us 

X=2^16-100000/2=65536-50000=15536=3CB0H. 

We get: TH1=3CH, TL1=0B0H 

3. Mode 2 

When bit M1M0=10. T is an 8-bit counter that automatically reloads the initial value. The count is in TLi. When TL overflows, not only TF=1, but also the value in TH is automatically sent to TL, and the value of TH remains unchanged. 

If the design value is N, then the initial value of the count is X=2^8-N; 2^8=256=100H. 

Example 3: If fosc=6MHz, and it is required to use T1 mode 2 for 500us, find the initial values ​​of TH1 and TL1. 

The initial value of the design number is X; from the known conditions, we get: 1 machine cycle = 12/fosc=2us; 

500us=12/fosc*(2^8-X)us 

X=2^8-500/2=256-250=6, 

so: TH1=6H, TL1=6H, in fact, just assign an initial value to TH. 

4. Mode 3 

When bit M1M0=11. Only T0 has mode 3. If T1 is set to mode 3, it will stop working. 

When T0 is in mode 3, TH0 and TL0 become two independent 8-bit counters; TL0 uses T0's control resources: GATE, C//T, TR0, TF0, /INT0 pin, etc., and can be used as an 8-bit timer/counter, while TH0 occupies T1's TR1 and TF1, and is a fixed 8-bit timer. At this time, T1 is controlled by the mode bit, mode 3 stops, and modes 0~2 are allowed to work, but TF1 is not set to 1 when the count overflows, that is, an interrupt request cannot be generated. In this case, T1 is generally used as a baud rate generator for the serial port.