NXP Semiconductors LPC43 Series User Manual

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NXP Semiconductors LPC43 Series User Manual Manual pdf 979 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 979 of 1269NXP Semiconductors UM10503Chapter 37: LPC43xx USART0_2_3During synchronous master mode, when start and stop bits are transmitted, the user canenable the external clock continuously using cscen bit of the Synchronous Mode Controlregister. This allows the connected slave to transmit data even when no data istransmitted by the master itself.37.7.6 Smart card modeFigure 117 shows a typical asynchronous smart card application.When the SCIEN bit in the SCICTRL register (Table 839) is set as described above, theUSART provides bidirectional serial data on the open-drain TXD pin. No RXD pin is usedwhen SCIEN is 1. The USART UCLK pin will output synchronously with the data at thedata bit rate. Software must use timers to implement character and block waiting times (nohardware support via trigger signals is provided on this part). GPIO pins can be used tocontrol the smart card reset and power pins. Any power supplied to the card must beexternally switched as card power supply requirements often exceed source currentspossible on this part. As the specific application may accommodate any of the availableISO 7816 class A, B, or C power requirements, be aware of the logic level tolerances andrequirements when communicating or powering cards that use different power rails thanthis part.37.7.6.1 Smart card set-up procedureA T = 0 protocol transfer consists of 8-bits of data, an even parity bit, and two guard bitsthat allow for the receiver of the particular transfer to flag parity errors through the NACKresponse (see Figure 118). Extra guard bits may be added according to cardrequirements. If no NACK is sent (provided the interface accepts them in SCICTRL), thenext byte may be transmitted immediately after the last guard bit. If the NACK is sent, thetransmitter will retry sending the byte until successfully received or until the SCICTRLretry limit has been met.Fig 117. Typical smart card applicationLPCxxxx ISO 7816Smart Cardpull-upresistorselectablepower railVCCCLKI/ORSTInsertion SwitchOptionalLogic LevelTranslationpull-upresistorpull-upresistorGPIOGPIOGPIOTXDUCLK