NXP Semiconductors LPC43 Series User Manual

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NXP Semiconductors LPC43 Series User Manual Manual pdf 964 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 964 of 1269NXP Semiconductors UM10503Chapter 37: LPC43xx USART0_2_3This register controls the clock pre-scaler for the baud rate generation. The reset value ofthe register keeps the fractional capabilities of USART disabled making sure that USARTis fully software and hardware compatible with USARTs not equipped with this feature.The USART baud rate can be calculated as:(6)Where USART_PCLK is the peripheral clock, DLM and DLL are the standard USARTbaud rate divider registers, and DIVADDVAL and MULVAL are USART fractional baudrate generator specific parameters.The value of MULVAL and DIVADDVAL should comply to the following conditions:1. 1 MULVAL  152. 0  DIVADDVAL  143. DIVADDVAL< MULVALThe value of the FDR should not be modified while transmitting/receiving data or data maybe lost or corrupted.If the FDR register value does not comply to these two requests, then the fractional divideroutput is undefined. If DIVADDVAL is zero then the fractional divider is disabled, and theclock will not be divided.37.6.13 USART Oversampling RegisterIn most applications, the USART samples received data 16 times in each nominal bit timeand sends bits that are 16 input clocks wide. This register allows software to control theratio between the input clock and bit clock. Oversampling is required for smart card modeand provides an alternative to fractional division for other modes.Table 836. USART Fractional Divider Register (FDR - addresses 0x4008 1028 (USART0),0x400C 1028 (USART2), 0x400C 2028 (USART3)) bit descriptionBit Function Description Resetvalue3:0 DIVADDVAL Baud rate generation pre-scaler divisor value.If this field is 0, fractional baud rate generator will not impact theUSART baud rate.07:4 MULVAL Baud rate pre-scaler multiplier value.This field must be greater or equal 1 for USART to operateproperly, regardless of whether the fractional baud rategenerator is used or not.131:8 - Reserved, user software should not write ones to reserved bits.The value read from a reserved bit is not defined.0UART baudratePCLK16 256 DLM DLL+  1 DivAddValMulVal-----------------------------+  ------------------------------------------------------------------------------------------------------------------=