ST
Address
SP ST
Data
SP
ST
Data
SP
Blocks of
characters
Idle periods of no significance
UCAxTXD, UCAxRXD
Expanded
UCAxTXD
UCAxRXD
First character within block
is an address, AD bit is 1
AD bit is 0 for
data within block
Idle time is of no significance
UCAxTXD
UCAxRXD
1
0
0
eUSCI_A Operation – UART Mode
772
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
Enhanced Universal Serial Communication Interface (eUSCI) – UART Mode
30.3.3.2 Address-Bit Multiprocessor Format
When UCMODEx = 10, the address-bit multiprocessor format is selected. Each processed character
contains an extra bit used as an address indicator (see
). The first character in a block of
characters carries a set address bit that indicates that the character is an address. The eUSCI_A
UCADDR bit is set when a received character has its address bit set and is transferred to UCAxRXBUF.
The UCDORM bit is used to control data reception in the address-bit multiprocessor format. When
UCDORM is set, data characters with address bit = 0 are assembled by the receiver but are not
transferred to UCAxRXBUF and no interrupts are generated. When a character containing a set address
bit 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 a character containing a set address bit 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 with address bit = 1 are received. The
UCDORM bit is not modified by the eUSCI_A hardware automatically.
When UCDORM = 0, all received characters set the receive interrupt flag UCRXIFG. If UCDORM is
cleared during the reception of a character, the receive interrupt flag is set after the reception is
completed.
For address transmission in address-bit multiprocessor mode, the address bit of a character is controlled
by the UCTXADDR bit. The value of the UCTXADDR bit is loaded into the address bit of the character
transferred from UCAxTXBUF to the transmit shift register. UCTXADDR is automatically cleared when the
start bit is generated.
Figure 30-4. Address-Bit Multiprocessor Format
30.3.3.2.1 Break Reception and Generation
When UCMODEx = 00, 01, or 10, the receiver detects a break when all data, parity, and stop bits are low,
regardless of the parity, address mode, or other character settings. When a break is detected, the UCBRK
bit is set. If the break interrupt enable bit (UCBRKIE) is set, the receive interrupt flag UCRXIFG is also set.
In this case, the value in UCAxRXBUF is 0h, because all data bits were zero.
To transmit a break, set the UCTXBRK bit, then write 0h to UCAxTXBUF. UCAxTXBUF must be ready for
new data (UCTXIFG = 1). This generates a break with all bits low. UCTXBRK is automatically cleared
when the start bit is generated.