Idea Ripper // ArchiveCards: 1555 [Live] | Updated: 2026-10-14
Card #c525IR // #c525Synthesis

In the 8-bit asynchronous mode, every byte is framed with one start bit, eight data bits, and one stop bit. SBUF is the byte register; SCON controls the mode; TI fires when the stop bit has been transmitted and RI fires when a full byte lands — and the CPU must clear both flags itself, or the handshake stalls. Baud comes from Timer 1 running in mode 2, so at 11.0592 MHz the reload values TH1 = FDH, FAH, F4H, and E8H give 9600, 4800, 2400, and 1200 baud respectively.

— In our words · Source: 8051 Microcontroller Notes

[Use when]

Bringing up an 8051 UART link — verify the framing in SCON, confirm Timer 1 mode 2 with the right TH1 reload, and always clear TI/RI in the handler before doing anything else.

[Why it matters]

The notes present serial communication as three cooperating mechanisms — framing, flags, and a timer-derived clock — and the load-bearing detail is that the CPU, not the hardware, owns TI/RI; forgetting to clear them is a silent deadlock.

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