The document discusses the timers and timer modes of the 8051 microcontroller. It has two 16-bit timers, Timer 0 and Timer 1, each made up of two 8-bit registers TH and TL. The TMOD register sets the timer modes and operations, while TCON controls the timer run/stop bits. There are four timer modes - mode 0 is a 13-bit timer, mode 1 is a 16-bit timer, mode 2 is an 8-bit auto-reload timer, and mode 3 splits timer 0 into two 8-bit timers using TH0 and TL0.

1. TIMER

5. TMODE TIMER 1 TIMER 0 M0 M1 C/ T GATE M0 M1 C/ T GATE

7. TIMER MODES Split mode 3 1 1 8 bit auto reload 2 0 1 16 bit timer 1 1 0 13 bit timer 0 0 0 OPERATIONS MODE M0 M1

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