SPRUJF2A March 2026 – March 2026 AM13E23019
This section applies to UNICOMM-UART configurations which support the UART-IDLELINE-MULTIPROC feature.
When IDLELINE is set in the CTL0.MODE register bits, the idle-line multiprocessor format is selected. Blocks of data are separated by an idle time on the transmit or receive lines (Figure 23-13). An idle receive line is detected when ten or more continuous ones (marks) are received after the one or two stop bits of a character. The baud-rate generator is switched off after reception of an idle line until the next start edge is detected. When an idle line is detected, the IDLE bit in UARTx.STAT is set. In Idle-Line mode the UART receiver operates in no parity mode and the UART word length (UARTx.LCRH.WLEN) must be set to 8bit.
The first character received after an idle period is an address character. The IDLE bit in UARTx.STAT register is used as an address tag for each block of characters.
If an address character is received it is compared against the ADDR register with the AMASK applied. If the received character matches, the address character and all following received characters are transferred into the RXDATA buffer/FIFO and interrupts are generated until the next address without a match is received. The IDLE bit in STAT register is automatically cleared when the address does match; otherwise the IDLE bit is set until the address is matched.
When SENDIDLE control bit is set, the UART inserts an idle period of 11 bit times on the bus. Application has to ensure that there are no active transactions on the transmit line prior to setting SENDIDLE bit.
Once SENDIDLE bit is set, application has to wait for SENDIDLE status bit to be asserted and then clear the SENDIDLE control bit to proceed. The next transfer can then begin with an address character.
The following procedure sends out an idle frame to indicate an address character followed by associated data:
The idle-line time (10 bit periods) must not be exceeded between address and data transmission or between data transmissions. Otherwise, the transmitted data is misinterpreted as an address.
When using IDLELINE mode, the UART Word Length in the LCRH register must be set to:
8-bit word length (WLEN bits 6:5 configured to 0x3)
BUSY bit in IDLELINE:
TX: BUSY is set during the generation of an IDLELINE signal and while the address and data bytes are sent.
RX: The BUSY signal while receiving data and till first 10 idle bits are received.