
DR
AFT
DR
AFT
DRAFT
DR
D
RAFT
DRAFT
DRA
FT DRAF
D
RAFT DRAFT DRAFT DRAFT DRAFT D
DRAFT
D
RAFT DRA
FT DRAFT DRAFT DRAFT DRA
UM10360_0
© NXP B.V. 2009. All rights reserved.
User manual
Rev. 00.06 — 5 June 2009
281 of 808
NXP Semiconductors
UM10360
Chapter 14: LPC17xx UART0/2/3
14.4.10.1 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.
•
The UnIIR ABTOInt interrupt will get set if the interrupt is enabled (UnIER ABToIntEn
is set and the auto-baud rate measurement counter overflows).
•
The UnIIR ABEOInt interrupt will get set if the interrupt is enabled (UnIER ABEOIntEn
is set and the auto-baud has completed successfully).
The auto-baud interrupts have to be cleared by setting the corresponding UnACR
ABTOIntClr and ABEOIntEn bits.
Typically the fractional baud-rate generator is disabled (DIVADDVAL = 0) during
auto-baud. However, if the fractional baud-rate generator is enabled (DIVADDVAL > 0), it
is going to impact the measuring of UARTn Rx pin baud-rate, but the value of the UnFDR
register is not going to be modified after rate measurement. Also, when auto-baud is used,
2
AutoRestart 0
No restart.
0
1
Restart in case of time-out (counter restarts at next
UARTn 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
Table 260: UARTn Auto-baud Control Register (U0ACR - address 0x4000 C020, U2ACR -
0x4009 8020, U3ACR - 0x4009 C020) bit description
Bit
Symbol
Value Description
Reset value