Auto-Baud Modes; User Manual - Philips LPC2101 User Manual

Philips Semiconductors
Volume 1

9.3.15 Auto-baud modes

When the software is expecting an "AT" command, it configures the UART0 with the
expected character format and sets the U0ACR Start bit. The initial values in the divisor
latches U0DLM and U0DLM don't care. Because of the "A" or "a" ASCII coding
("A" = 0x41, "a" = 0x61), the UART0 Rx pin sensed start bit and the LSB of the expected
character are delimited by two falling edges. When the U0ACR Start bit is set, the
auto-baud protocol will execute the following phases:

User manual

1. On U0ACR Start bit setting, the baud-rate measurement counter is reset and the
UART0 U0RSR is reset. The U0RSR baud rate is switch to the highest rate.
2. A falling edge on UART0 Rx pin triggers the beginning of the start bit. The rate
measuring counter will start counting PCLK cycles optionally pre-scaled by the
fractional baud-rate generator.
3. During the receipt of the start bit, 16 pulses are generated on the RSR baud input with
the frequency of the (fractional baud-rate pre-scaled) UART0 input clock,
guaranteeing the start bit is stored in the U0RSR.
4. During the receipt of the start bit (and the character LSB for mode = 0) the rate
counter will continue incrementing with the pre-scaled UART0 input clock (PCLK).
5. If Mode = 0 then the rate counter will stop on next falling edge of the UART0 Rx pin. If
Mode = 1 then the rate counter will stop on the next rising edge of the UART0 Rx pin.
6. The rate counter is loaded into U0DLM/U0DLL and the baud-rate will be switched to
normal operation. After setting the U0DLM/U0DLL the end of auto-baud interrupt
U0IIR ABEOInt will be set, if enabled. The U0RSR will now continue receiving the
remaining bits of the "A/a" character.
Rev. 01 — 12 January 2006
UM10161
Chapter 9: UART0
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
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