UARTx_ET7816 field descriptions (continued)Field DescriptionRXTHRESHOLD Receive NACK ThresholdThe value written to this field indicates the maximum number of consecutive NACKs generated as a resultof a parity error or receiver buffer overruns before the host processor is notified. After the counter exceedsthat value in the field, the IS7816[RXT] is asserted. This field is meaningful only when C7816[TTYPE] = 0.The value read from this field represents the number of consecutive NACKs that have been transmittedsince the last successful reception. This counter saturates at 4'hF and does not wrap around. Regardlessof the number of NACKs sent, the UART continues to receive valid packets indefinitely. For additionalinformation, see IS7816[RXT] field description.38.4.20 UART 7816 Transmit Length Register (UARTx_TL7816)The TL7816 register is used to indicate the number of characters contained in the blockbeing transmitted. This register is used only when C7816[TTYPE] = 1. This register maybe read at anytime. This register must be written only when C2[TE] is not enabled.Address: 4006_C000h base + 1Fh offset = 4006_C01FhBit 7 6 5 4 3 2 1 0Read TLENWriteReset 0 0 0 0 0 0 0 0UARTx_TL7816 field descriptionsField DescriptionTLEN Transmit LengthThis value plus four indicates the number of characters contained in the block being transmitted. Thisregister is automatically decremented by 1 for each character in the information field portion of the block.Additionally, this register is automatically decremented by 1 for the first character of a CRC in the epiloguefield. Therefore, this register must be programmed with the number of bytes in the data packet if an LRC isbeing transmitted, and the number of bytes + 1 if a CRC is being transmitted. This register is notdecremented for characters that are assumed to be part of the Prologue field, that is, the first threecharacters transmitted in a block, or the LRC or last CRC character in the Epilogue field, that is, the lastcharacter transmitted. This field must be programed or adjusted only when C2[TE] is cleared.38.4.21 UART 7816 ATR Duration Timer Register A(UARTx_AP7816A_T0)The AP7816A_T0 register contains variables used in the generation of the ATR DurationTimer. This register may be read at any time. This register must be written to only whenC7816[ISO_7816E] is not set, except when writing 0 to clear the ADT Counter.Chapter 38 Universal Asynchronous Receiver/Transmitter(UART)KL27 Sub-Family Reference Manual , Rev. 5, 01/2016Freescale Semiconductor, Inc. 703
