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SC16IS740 Datasheet(PDF) 18 Page - NXP Semiconductors |
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SC16IS740 Datasheet(HTML) 18 Page - NXP Semiconductors |
18 / 63 page SC16IS740_750_760 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved. Product data sheet Rev. 7 — 9 June 2011 18 of 63 NXP Semiconductors SC16IS740/750/760 Single UART with I2C-bus/SPI interface, 64-byte FIFOs, IrDA SIR 7.8 Programmable baud rate generator The SC16IS740/750/760 UART contains a programmable baud rate generator that takes any clock input and divides it by a divisor in the range between 1 and (216 –1). An additional divide-by-4 prescaler is also available and can be selected by MCR[7], as shown in Figure 15. The output frequency of the baud rate generator is 16 the baud rate. The formula for the divisor is given in Equation 1: (1) where: prescaler = 1, when MCR[7] is set to ‘0’ after reset (divide-by-1 clock selected) prescaler = 4, when MCR[7] is set to ‘1’ after reset (divide-by-4 clock selected). Remark: The default value of prescaler after reset is divide-by-1. Figure 15 shows the internal prescaler and baud rate generator circuitry. DLL and DLH must be written to in order to program the baud rate. DLL and DLH are the least significant and most significant byte of the baud rate divisor. If DLL and DLH are both zero, the UART is effectively disabled, as no baud clock will be generated. Remark: The programmable baud rate generator is provided to select both the transmit and receive clock rates. Table 7 and Table 8 show the baud rate and divisor correlation for crystal with frequency 1.8432 MHz and 3.072 MHz, respectively. The crystal’s frequency tolerance should be selected as such to keep the baud rate error to be below 1 % for reliable operation with other UARTs. Crystals with 100 ppm is generally recommended. Figure 16 shows the crystal clock circuit reference. Fig 15. Prescaler and baud rate generator block diagram divisor XTAL1 crystal input frequency prescaler ----------------------------------------------------------------------------------- desired baud rate 16 ----------------------------------------------------------------------------------------- = BAUD RATE GENERATOR LOGIC MCR[7] = 1 MCR[7] = 0 PRESCALER LOGIC (DIVIDE-BY-1) INTERNAL OSCILLATOR LOGIC 002aaa233 XTAL1 XTAL2 input clock PRESCALER LOGIC (DIVIDE-BY-4) reference clock internal baud rate clock for transmitter and receiver |
Similar Part No. - SC16IS740_11 |
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Similar Description - SC16IS740_11 |
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