UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
165 of 362
NXP Semiconductors
UM10208
Chapter 14: LPC2800 UART
3.15 Auto-baud Control Register (ACR - 0x8010 1020)
The Auto-baud Control Register (ACR) controls the process of measuring the incoming
clock/data rate for baud rate generation.
3.15.1 Auto-baud
The auto-baud function can be used to measure the incoming baud rate based on the
”AT" protocol (Hayes command set). If enabled the auto-baud feature measures the
duration of the first 1 or 2 bits on RXD and sets the divisor latch registers DLM and DLL
accordingly.
Auto-baud is started by setting the ACR_Start bit. Auto-baud can be stopped by clearing
the ACR_Start bit. The ACR_Start bit will clear once auto-baud has finished, and reading
the bit will return the status of auto-baud (in progress / finished).
Two auto-baud measuring modes are available, based on the ACR_Mode bit. In mode 0
the baud rate is measured on two subsequent falling edges of the RXD 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 RXD pin
(the length of the start bit). If the next character on RXD is an "A" as in an "AT command",
either mode can be used.
The ACR 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 RXD pin.
The auto-baud function can generate two interrupts.
•
The IIR ABTOInt interrupt will get set if the interrupt is enabled (IER ABToIntEn is set
and the auto-baud rate measurement counter overflows).
•
The IIR ABEOInt interrupt will get set if the interrupt is enabled (IER ABEOIntEn is set
and the auto-baud has completed successfully).
Table 181. Auto-baud Control Register (ACR - 0x8010 1020)
Bit
Name
Description
Reset
value
0
ACR_Start
Software should write a 1 to this bit to initiate auto-baud
measurement. This bit is automatically cleared after auto-baud
completion.
0
1
ACR_Mode
Auto-baud mode select bit. See
below.
0
2
AutoRestart A 1 in this bit causes a restart in case of time-out. (The counter
restarts at the next RXD falling edge.)
0
7:3
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-
8
ABEOIntClr
Software should write a 1 to this bit to clear the End of auto-baud
interrupt bit in the IIR. Writing a 0 has no impact. This bit always
reads as 0.
0
9
ABTOIntClr
Software should write a 1 to this bit to clear the Auto-baud time-out
interrupt bit in the IIR. Writing a 0 has no impact. This bit always
reads as 0.
0
31:10 -
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
-