Information

UARTx_ET7816 field descriptions (continued)
Field Description
The value written to this field indicates the maximum number of failed attempts (NACKs) a transmitted
character can have before the host processor is notified. Meaning a value of 0 will always result in TXT
asserting on the first NACK that is received. A value of 1 will result in TXT being asserted on the second
NACK that is received. This field is only meaningful when C7816[TTYPE] = 0 and C7816[ANACK] = 1.
The value read from this field represents the number of consecutive NACKs that have been received
since the last successful transmission. This counter saturates at 4'hF and does not wrap around.
Regardless of how many NACKs that are received, the UART will continue to retransmit indefinitely. This
flag only asserts when C7816[TTYPE] = 0. For additional information see the IS7816[TXT] bit description.
3–0
RXTHRESHOLD
Receive NACK Threshold
The value written to this field indicates the maximum number of consecutive NACKs generated as a result
of a parity error or receiver buffer overruns before the host processor is notified. Once the counter
exceeds that value in the field the IS7816[RXT] will be asserted. This field is only meaningful when
C7816[TTYPE] = 0. The value read from this field represents the number of consecutive NACKs that have
been transmitted since the last successful reception. This counter saturates at 4'hF and does not wrap
around. Regardless of the number of NACKs sent, the UART will continue to receive valid packets
indefinitely. For additional information see IS7816[RXT] bit description.
48.3.31 UART 7816 Transmit Length Register (UARTx_TL7816)
The TL7816 register is used to indicate how many characters are contained in the block
being transmitted. This register is only used when C7816[TTYPE] = 1. This register may
be read at anytime. This register should only be written when C2[TE] is not enabled.
Addresses: UART0_TL7816 is 4006_A000h base + 1Fh offset = 4006_A01Fh
UART1_TL7816 is 4006_B000h base + 1Fh offset = 4006_B01Fh
UART2_TL7816 is 4006_C000h base + 1Fh offset = 4006_C01Fh
UART3_TL7816 is 4006_D000h base + 1Fh offset = 4006_D01Fh
Bit 7 6 5 4 3 2 1 0
Read
TLEN
Write
Reset
0 0 0 0 0 0 0 0
UARTx_TL7816 field descriptions
Field Description
7–0
TLEN
Transmit Length
This value plus 4 indicates the number of characters contained in the block being transmitted. This
register 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 epilogue
field. Hence, this register should be programmed with the number of bytes in the data packet if a LRC is
being transmitted, and the number of bytes + 1 if a CRC is being transmitted. This register is not
decremented for characters that are assumed to be part of the Prologue field (first three characters
transmitted in a block) or the LRC or last CRC character in the Epilogue field (last character transmitted).
This field should only be programed or adjusted when C2[TE] is cleared.
Memory map and registers
K20 Sub-Family Reference Manual, Rev. 6, Nov 2011
1334 Freescale Semiconductor, Inc.