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Card #c524IR // #c524Synthesis

One machine cycle is 12 oscillator periods (1.085 us at 11.0592 MHz), and that heartbeat feeds Timer 0 and Timer 1. The TMOD register splits control between them — the lower nibble configures Timer 0, the upper nibble Timer 1 — each timer counts in THx/TLx, raises the TFx flag on overflow, and is started or stopped with TRx. Mode 1 is a 16-bit counter that must be reloaded by hand after every overflow; Mode 2 is 8-bit auto-reload, where TH holds the reload value and TL counts and silently reloads on overflow.

— In our words · Source: 8051 Microcontroller Notes

[Use when]

Generating a delay, square wave, or baud clock on the 8051 — pick the mode whose reload discipline fits the job, then compute the TH/TL values from the 1.085 us heartbeat.

[Why it matters]

The notes hammer one insight: precision timing on a tiny chip is not about speed, it is about the reload discipline — mode choice decides whether you pay a reload cost per tick or let the hardware do it, which is exactly how the notes generate baud rates and square waves.

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