provide configuration options that exceed the flexibility ofoptions explicitly allowed by the 7816 specification. Failure tocorrectly configure the UART may result in unexpectedbehavior or incompatibility with the ISO-7816 specification.38.5.7.1 Initial charactersIn ISO-7816 with T = 0 mode, the UART can be configured to use C7816[INIT] to detectthe next valid initial character, referred to by the ISO-7816 specifically as a TS character.When the initial character is detected, the UART provides the host processor with aninterrupt if IE7816[INITDE] is set. Additionally, the UART will alter S2[MSBF],C3[TXINV], and S2[RXINV] automatically, based on the initial character. Thecorresponding initial character and resulting register settings are listed in the followingtable.Table 38-12. Initial character automated settingsInitial character (bit 1-10) Initial character(hex) MSBF TXINV RXINVLHHL LLL LLHinverse convention3F 1 1 1LHHL HHH LLHdirect convention3B 0 0 0S2[MSBF], C3[TXINV], and S2[RXINV] must be reset to their default values beforeC7816[INIT] is set. Once C7816[INIT] is set, the receiver searches all received data forthe first valid initial character. Detecting a Direct Convention Initial Character will causeno change to S2[MSBF], C3[TXINV], and S2[RXINV], while detecting an InverseConvention Initial Character will cause these fields to set automatically. All datareceived, which is not a valid initial character, is ignored and all flags resulting from theinvalid data are blocked from asserting. If C7816[ANACK] is set, a NACK is returnedfor invalid received initial characters and an RXT interrupt is generated as programmed.38.5.7.2 Protocol T = 0When T = 0 protocol is selected, a relatively complex error detection scheme is used.Data characters are formatted as illustrated in the following figure. This scheme is alsoused for answer to reset and Peripheral Pin Select (PPS) formats.Chapter 38 Universal Asynchronous Receiver/Transmitter(UART)KL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 731
