TCON control word and TMOD register

TCON: Timer Control Register

Register address 88H, bit addressing 8FH～88H

TF0(TF1)——Count overflow flag, when the counter overflows, this position is 1.

TR0 (TR1) - timer operation control bit

When TR0 (TR1) = 0, stop the timer/counter

When TR0 (TR1) = 1, the timer/counter starts working.

IE0 (IE1) - External interrupt request flag

When the CPU samples P3.2 (P3.3) and detects a valid interrupt request, this bit is set to 1 by hardware. After the interrupt response is completed and the interrupt service is turned to, it is automatically cleared to 0 by hardware.

IT0 (IT1) - External interrupt request signal mode control bit

When IT0 (IT1) = 1, pulse mode (negative edge jump is valid)

When IT0 (IT1) = 0 level mode (low level is valid), this bit is set or cleared by software.

TF0 (TF1)——Count overflow flag

When the counter overflows, this bit is set to 1 by hardware. When the interrupt service is turned, the hardware automatically clears it to 0. There are two situations for using the overflow flag: when the interrupt mode is used, it is used as an interrupt request flag; when the query mode is used, it is used as a query status bit.

TMOD register Timer/counter T0￤T1 mode register 

The lower four bits define timer/counter T0, and the upper four bits define timer/counter T1. Explanation of each bit:

Ⅰ, GATE - Gate control.
When GATE = 1, the timer is started by the external interrupt pins INT0, INT1 and the control register TR0, TR1.

When GATE=0, timers T0 and T1 are started only by setting TR0 and TR1.
Ⅱ, C/T - Function selection bit

　　When set, select the counting function, and when cleared, select the timing function.

　Ⅲ, M0, M1——Mode selection function

　　Since there are 2 bits, there are 4 ways to work

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　　M1M0 working mode counter mode TMOD (set timer mode)

　　0 0 Mode 0 13-bit counter TMOD = 0x00

　　0 1 Mode 1 16-bit counter TMOD = 0x01

　　1 0 Mode 2 Automatically reload 8-bit counter TMOD=0x02

　　1 1 Mode 3 T0 is divided into two 8-bit counters, T1 is the baud rate generator TMOD=0x03

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