NXP Semiconductors K22F series, Reference Manual, Page: 1248 / 1407

UARTx_C7816 field descriptions
Field Description
7–5
Reserved
This field is reserved.
This read-only field is reserved and always has the value 0.
4
ONACK
Generate NACK on Overflow
When this field is set, the receiver automatically generates a NACK response if a receive buffer overrun
occurs, as indicated by S1[OR]. In many systems, this results in the transmitter resending the packet that
overflowed until the retransmit threshold for that transmitter is reached. A NACK is generated only if
TTYPE=0. This field operates independently of ANACK. See .
Overrun NACK considerations
0 The received data does not generate a NACK when the receipt of the data results in an overflow
event.
1 If the receiver buffer overflows, a NACK is automatically sent on a received character.
3
ANACK
Generate NACK on Error
When this field is set, the receiver automatically generates a NACK response if a parity error occurs or if
INIT is set and an invalid initial character is detected. A NACK is generated only if TTYPE = 0. If ANACK is
set, the UART attempts to retransmit the data indefinitely. To stop retransmission attempts, clear C2[TE]
or ISO_7816E and do not set until S1[TC] sets C2[TE] again.
0 No NACK is automatically generated.
1 A NACK is automatically generated if a parity error is detected or if an invalid initial character is
detected.
2
INIT
Detect Initial Character
When this field is set, all received characters are searched for a valid initial character. If an invalid initial
character is identified, and ANACK is set, a NACK is sent. All received data is discarded and error flags
blocked (S1[NF], S1[OR], S1[FE], S1[PF], IS7816[WT], IS7816[CWT], IS7816[BWT], IS7816[ADT],
IS7816[GTV]) until a valid initial character is detected. Upon detecting a valid initial character, the
configuration values S2[MSBF], C3[TXINV], and S2[RXINV] are automatically updated to reflect the initial
character that was received. The actual INIT data value is not stored in the receive buffer. Additionally,
upon detection of a valid initial character, IS7816[INITD] is set and an interrupt issued as programmed by
IE7816[INITDE]. When a valid initial character is detected, INIT is automatically cleared. This Initial
Character Detect feature is supported only in T = 0 protocol mode.
0 Normal operating mode. Receiver does not seek to identify initial character.
1 Receiver searches for initial character.
1
TTYPE
Transfer Type
Indicates the transfer protocol being used.
See ISO-7816 / smartcard support for more details.
0 T = 0 per the ISO-7816 specification.
1 T = 1 per the ISO-7816 specification.
0
ISO_7816E
ISO-7816 Functionality Enabled
Indicates that the UART is operating according to the ISO-7816 protocol.
NOTE: This field must be modified only when no transmit or receive is occurring. If this field is changed
during a data transfer, the data being transmitted or received may be transferred incorrectly.
0 ISO-7816 functionality is turned off/not enabled.
1 ISO-7816 functionality is turned on/enabled.
Memory map and registers
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1248 NXP Semiconductors