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UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
306 of 808
NXP Semiconductors
UM10360
Chapter 15: LPC17xx UART1
4.14 Auto-baud
The UART1 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 U1DLM and U1DLL
accordingly.
Auto-baud is started by setting the U1ACR Start bit. Auto-baud can be stopped by clearing
the U1ACR 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 U1ACR
Mode bit. In mode 0 the baud-rate is measured on two subsequent falling edges of the
UART1 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 UART1 Rx pin (the length of the start bit).
Table 283: Auto-baud Control Register (U1ACR - address 0x4001 0020) 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
UART1 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).
0
0
Writing a 0 has no impact.
1
Writing a 1 will clear the corresponding interrupt in the
U1IIR.
9
ABTOIntClr
Auto-baud time-out interrupt clear bit (write only
accessible).
0
0
Writing a 0 has no impact.
1
Writing a 1 will clear the corresponding interrupt in the
U1IIR.
31:10 -
NA
Reserved, user software should not write ones to
reserved bits. The value read from a reserved bit is not
defined.
0