UCAxTXD
UCAxRXD
UCAxTXD
UCAxRXD
UCAxTXD or UCAxRXD
Expanded
First character in block is
address, and it follows an
Idle period of 10 bits or more
Idle periods of 10 bits or more
Idle period fewer than 10 bits
Character within block
Character within block
Blocks of
characters
eUSCI_A Operation – UART Mode
771
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Enhanced Universal Serial Communication Interface (eUSCI) – UART Mode
The first character received after an idle period is an address character. The UCIDLE bit is used as an
address tag for each block of characters. In idle-line multiprocessor format, this bit is set when a received
character is an address.
Figure 30-3. Idle-Line Format
The UCDORM bit is used to control data reception in the idle-line multiprocessor format. When UCDORM
= 1, all non-address characters are assembled but not transferred into the UCAxRXBUF, and interrupts
are not generated. When an address character is received, the character is transferred into UCAxRXBUF,
UCRXIFG is set, and any applicable error flag is set when UCRXEIE = 1. When UCRXEIE = 0 and an
address character is received but has a framing error or parity error, the character is not transferred into
UCAxRXBUF and UCRXIFG is not set.
If an address is received, user software can validate the address and must reset UCDORM to continue
receiving data. If UCDORM remains set, only address characters are received. When UCDORM is cleared
during the reception of a character, the receive interrupt flag is set after the reception completed. The
UCDORM bit is not modified automatically by the eUSCI_A hardware.
For address transmission in idle-line multiprocessor format, a precise idle period can be generated by the
eUSCI_A to generate address character identifiers on UCAxTXD. The double-buffered UCTXADDR flag
indicates if the next character loaded into UCAxTXBUF is preceded by an idle line of 11 bits. UCTXADDR
is automatically cleared when the start bit is generated.
30.3.3.1.1 Transmitting an Idle Frame
The following procedure sends out an idle frame to indicate an address character followed by associated
data:
1. Set UCTXADDR, then write the address character to UCAxTXBUF. UCAxTXBUF must be ready for
new data (UCTXIFG = 1).
This generates an idle period of exactly 11 bits followed by the address character. UCTXADDR is reset
automatically when the address character is transferred from UCAxTXBUF into the shift register.
2. Write desired data characters to UCAxTXBUF. UCAxTXBUF must be ready for new data
(UCTXIFG = 1).
The data written to UCAxTXBUF is transferred to the shift register and transmitted as soon as the shift
register is ready for new data.
The idle-line time must not be exceeded between address and data transmission or between data
transmissions. Otherwise, the transmitted data is misinterpreted as an address.