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UM10316_0
© NXP B.V. 2008. All rights reserved.
User manual
Rev. 00.06 — 17 December 2008
285 of 571
NXP Semiconductors
UM10316
Chapter 19: LPC29xx Universal Asynchronous Receiver/Transmitter
4.12.1 Auto-baud
The UARTn auto-baud function can be used to measure the incoming baud-rate based on
the ”AT" protocol (Hayes command). If enabled the auto-baud feature will measure the bit
time of the receive data stream and set the divisor latch registers UnDLM and UnDLL
accordingly.
Auto-baud is started by setting the UnACR Start bit. Auto-baud can be stopped by clearing
the UnACR Start bit. The Start bit will clear once auto-baud has finished and reading the
bit will return the status of auto-baud (pending/finished).
Two auto-baud measuring modes are available which can be selected by the UnACR
Mode bit. In mode 0 the baud-rate is measured on two subsequent falling edges of the
UARTn Rx pin (the falling edge of the start bit and the falling edge of the least significant
bit). In mode 1 the baud-rate is measured between the falling edge and the subsequent
rising edge of the UARTn Rx pin (the length of the start bit).
The UnACR AutoRestart bit can be used to automatically restart baud-rate measurement
if a time-out occurs (the rate measurement counter overflows). If this bit is set the rate
measurement will restart at the next falling edge of the UARTn Rx pin.
The auto-baud function can generate two interrupts.
Table 243. UARTn Auto-baud Control Register (U0ACR - 0xE004 5020, U1ACR - 0xE004 6020)
bit description
Bit
Symbol
Value Description
Reset value
0
Start
This bit is automatically cleared after auto-baud
completion.
0
0
Auto-baud stop (auto-baud is not running).
1
Auto-baud start (auto-baud is running).Auto-baud run
bit. This bit is automatically cleared after auto-baud
completion.
1
Mode
Auto-baud mode select bit.
0
0
Mode 0.
1
Mode 1.
2
AutoRestart 0
No restart.
0
1
Restart in case of time-out (counter restarts at next
UART0 Rx falling edge)
0
7:3
-
NA
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
0
8
ABEOIntClr
End of auto-baud interrupt clear bit (write only
accessible). Writing a 1 will clear the corresponding
interrupt in the UnIIR. Writing a 0 has no impact.
0
9
ABTOIntClr
Auto-baud time-out interrupt clear bit (write only
accessible). Writing a 1 will clear the corresponding
interrupt in the UnIIR. Writing a 0 has no impact.
0
31:10 -
NA
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
0