UM10413
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User manual
Rev. 1 — 16 December 2011
90 of 268
NXP Semiconductors
UM10413
MPT612 User manual
14.3.14 Auto-baud modes
When the software is expecting an AT command, it configures the UART0 with the
expected character format and sets bit U0ACR Start. The initial values in the divisor
latches U0DLM and U0DLM are set to do not care. Because of the ”A" or ”a" ASCII coding
(”A" = 0x41, ”a" = 0x61), pin UART0 Rx sensed start bit and the LSB of the expected
character are delimited by two falling edges. When bit U0ACR Start is set, the auto-baud
protocol executes the following phases:
1. On setting bit U0ACR Start, the baud-rate measurement counter is reset and the
UART0 U0RSR is reset. The U0RSR baud rate is switched to the highest rate.
2. A falling edge on pin UART0 Rx triggers the beginning of the start bit. The rate
measuring counter starts counting PCLK cycles optionally pre-scaled by the fractional
baud rate generator.
3. During receipt of the start bit, 16 pulses are generated on baud input RSR at the
frequency of the (fractional baud rate pre-scaled) UART0 input clock, guaranteeing
the start bit is stored in U0RSR.
4. During the receipt of the start bit (and the character LSB for mode = 0), the rate
counter continues incrementing with the pre-scaled UART0 input clock (PCLK).
5. If Mode = 0, then the rate counter stops on the next falling edge of pin UART0 Rx. If
Mode = 1, then the rate counter stops on the next rising edge of pin UART0 Rx.
6. The rate counter is loaded into U0DLM/U0DLL and the baud rate is switched to
normal operation. After setting the U0DLM/U0DLL, the end of auto-baud interrupt
U0IIR ABEOInt is set, if enabled. The U0RSR continues receiving the remaining bits
of the ”A/a" character.
Table 97:
UART0 Transmit enable register (U0TER - address 0xE000 C030) bit description
Bit
Symbol
Description
Reset
value
6:0
-
reserved, user software must not write logic 1s to reserved bits; value
read from a reserved bit is not defined
n/a
7
TXEN
if logic 1, as it is after a reset, data written to THR is output on pin TXD
when any preceding data is sent. If cleared to logic 0 while a character
is being sent, transmission of that character is completed, no further
characters are sent until this bit is set again. In other words, if bit is
logic 0, it blocks transfer of characters from THR or Tx FIFO into
transmit shift register. Software implementing software-handshaking
can clear this bit when it receives an XOFF character (DC3). Software
can set this bit again when it receives an XON (DC1) character.
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