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USART Operation: UART Mode
13-7
USART Peripheral Interface, UART Mode
Address-Bit Multiprocessor Format
When MM = 1, the address-bit multiprocessor format is selected. Each
processed character contains an extra bit used as an address indicator shown
in Figure 13−4. The first character in a block of characters carries a set
address bit which indicates that the character is an address. The USART
RXWAKE bit is set when a received character is a valid address character and
is transferred to UxRXBUF.
The URXWIE bit is used to control data reception in the address-bit
multiprocessor format. If URXWIE is set, data characters (address bit = 0) are
assembled by the receiver but are not transferred to UxRXBUF and no
interrupts are generated. When a character containing a set address bit is
received, the receiver is temporarily activated to transfer the character to
UxRXBUF and set URXIFGx. All applicable error status flags are also set.
If an address is received, user software must reset URXWIE to continue
receiving data. If URXWIE remains set, only address characters (address bit
= 1) will be received. The URXWIE bit is not modified by the USART hardware
automatically.
Figure 13−4. Address-Bit Multiprocessor Format
ST Address SP ST Data SP ST Data S
P
Blocks of
Characters
Idle Periods of No Significance
UTXDx/URXDx
Expanded
UTXDx/URXDx
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
UTXDx/URXDx
1 0 0
For address transmission in address-bit multiprocessor mode, the address bit
of a character can be controlled by writing to the TXWAKE bit. The value of the
TXWAKE bit is loaded into the address bit of the character transferred from
UxTXBUF to the transmit shift register, automatically clearing the TXWAKE bit.
TXWAKE must not be cleared by software. It is cleared by USART hardware
after it is transferred to WUT or by setting SWRST.