UM10503
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User manual
Rev. 1.3 — 6 July 2012
971 of 1269
NXP Semiconductors
UM10503
Chapter 37: LPC43xx USART0_2_3
37.6.20 USART Transmit Enable Register
In addition to being equipped with full hardware flow control (auto-cts and auto-rts
mechanisms described above), TER enables implementation of software flow control.
When TxEn = 1, USART transmitter will keep sending data as long as they are available.
As soon as TxEn becomes 0, USART transmission will stop.
describes how to use TXEN bit in order to achieve software flow control.
37.7 Functional description
37.7.1 Auto-baud
The USART 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 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 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 ACR Mode
bit. In Mode 0 the baud rate is measured on two subsequent falling edges of the USART
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 USART Rx pin (the length of the start bit).
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 USART Rx 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).
The auto-baud interrupts have to be cleared by setting the corresponding ACR
ABTOIntClr and ABEOIntEn bits.
Table 844. USART Transmit Enable Register (TER - addresses 0x4008 105C (USART0),
0x400C 105C (USART2), 0x400C 205C (USART3)) bit description
Bit
Symbol
Description
Reset value
0
TXEN
Transmit enable.
After reset transmission is enabled. When the TXEN bit is
de-asserted, no data will be transmitted although data may be
pending in the TSR or THR.
1
31:1 -
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
-