NXP Semiconductors LPC43 Series User Manual

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NXP Semiconductors LPC43 Series User Manual Manual pdf 971 page image

UM10503 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2012. All rights reserved.User manual Rev. 1.3 — 6 July 2012 971 of 1269NXP Semiconductors UM10503Chapter 37: LPC43xx USART0_2_337.6.20 USART Transmit Enable RegisterIn addition to being equipped with full hardware flow control (auto-cts and auto-rtsmechanisms 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.Table 844 describes how to use TXEN bit in order to achieve software flow control.37.7 Functional description37.7.1 Auto-baudThe USART auto-baud function can be used to measure the incoming baud rate based onthe ”AT" protocol (Hayes command). If enabled the auto-baud feature will measure the bittime of the receive data stream and set the divisor latch registers DLM and DLLaccordingly.Auto-baud is started by setting the ACR Start bit. Auto-baud can be stopped by clearingthe ACR Start bit. The Start bit will clear once auto-baud has finished and reading the bitwill return the status of auto-baud (pending/finished).Two auto-baud measuring modes are available which can be selected by the ACR Modebit. In Mode 0 the baud rate is measured on two subsequent falling edges of the USARTRx pin (the falling edge of the start bit and the falling edge of the least significant bit). InMode 1 the baud rate is measured between the falling edge and the subsequent risingedge 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 atime-out occurs (the rate measurement counter overflows). If this bit is set, the ratemeasurement 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 setand the auto-baud rate measurement counter overflows).• The IIR ABEOInt interrupt will get set if the interrupt is enabled (IER ABEOIntEn is setand the auto-baud has completed successfully).The auto-baud interrupts have to be cleared by setting the corresponding ACRABTOIntClr and ABEOIntEn bits.Table 844. USART Transmit Enable Register (TER - addresses 0x4008 105C (USART0),0x400C 105C (USART2), 0x400C 205C (USART3)) bit descriptionBit Symbol Description Reset value0 TXEN Transmit enable.After reset transmission is enabled. When the TXEN bit isde-asserted, no data will be transmitted although data may bepending in the TSR or THR.131:1 - Reserved, user software should not write ones to reserved bits.The value read from a reserved bit is not defined.-