NXP Semiconductors freescale K51 Series Reference Manual

48.4.7.6 UART restrictions in ISO-7816 operationDue to the flexibility of the UART module, there are several features and interrupts thatare not supported while running in ISO-7816 mode. These restrictions are documentedwithin the register bit definitions.48.4.8 Infrared interfaceThe UART provides the capability of transmitting narrow pulses to an IR LED andreceiving narrow pulses and transforming them to serial bits, which are sent to theUART. The IrDA physical layer specification defines a half-duplex infraredcommunication link for exchanging data. The full standard includes data rates up to 16Mbits/s. This design covers data rates only between 2.4 kbits/s and 115.2 kbits/s.The UART has an infrared transmit encoder and receive decoder. The UART transmitsserial bits of data which are encoded by the infrared submodule to transmit a narrowpulse for every zero bit. No pulse is transmitted for every one bit. When receiving data,the IR pulses are detected using an IR photo diode and transformed to CMOS levels bythe IR receive decoder (external from the MCU). The narrow pulses are then stretched bythe infrared receive decoder to get back to a serial bit stream to be received by the UART.The polarity of transmitted pulses and expected receive pulses can be inverted so that adirect connection can be made to external IrDA transceiver modules that use active lowpulses.The infrared submodule receives its clock sources from the UART. One of these twoclocks are selected in the infrared submodule in order to generate either 3/16, 1/16, 1/32or 1/4 narrow pulses during transmission.48.4.8.1 Infrared transmit encoderThe infrared transmit encoder converts serial bits of data from transmit shift register tothe TXD signal. A narrow pulse is transmitted for a zero bit and no pulse for a one bit.The narrow pulse is sent in the middle of the bit with a duration of 1/32, 1/16, 3/16 or 1/4of a bit time. A narrow high pulse is transmitted for a zero bit when C3[TXINV] iscleared, while a narrow low pulse is transmitted for a zero bit when C3[TXINV] is set.Functional descriptionK51 Sub-Family Reference Manual, Rev. 6, Nov 20111290 Freescale Semiconductor, Inc.