3.3.6. SCIRETRY: [6] (+0x14)

SCIRETRY is the retry limit register and is used to configure the number of transmit and receive retries that are allowed.

If character transmit handshaking is enabled (TXNAK = 1), the TXRETRY field of this register contains a 3-bit value (0 to 2). This specifies the maximum number of attempts that can be made to retransmit a character that has been incorrectly received by the card, before aborting the transmission and generating a TXERR interrupt.

For normal T0 operation, the TXRETRY field should be set to 011 for a maximum of three retries. A value of 000 (no retries) causes a TXERR interrupt to occur as soon as an error is detected.

For T1 operation, character-based handshaking should be turned off (TXNAK = 0), in which case TXRETRY is not used.

The RXRETRY field of this register contains a 3-bit value (3 to 5). This specifies the maximum number of times the interface will request retransmission of a character after detection of a parity error.

For normal T0 operation, the RXRETRY field should be set to 011 for a maximum of three retries. A value of 000 (no retries) writes the received character to the receive FIFO with no request for retransmission in the event of a parity error. This has the same effect as setting RXNAK to 0.

If the character has not been successfully received after RXRETRY attempts, the parity error flag for that character is set. This appears as bit 8 of the SCIDATA register when it is read. Table 3.7 shows bit assignments for SCIRETRY.

Table 3.7. SCIRETRY register read/write bits

Bits

Name

Type

Function

5:3

RXRETRY

Read/write

Specifies the maximum number of retries to receive when a parity error has occurred in reception.

2:0

TXRETRY

Read/write

Specifies the maximum number of times that a character will be retransmitted following the detection of a parity error.

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