Figure 284. Mute Mode Using Idle Line Detection - ST STM32F101 series Reference Manual

RM0008
The non addressed devices may be placed in mute mode by means of the muting function.
In mute mode:
•
None of the reception status bits can be set.
•
All the receive interrupts are inhibited.
•
The RWU bit in USART_CR1 register is set to 1. RWU can be controlled automatically
by hardware or written by the software under certain conditions.
The USART can enter or exit from mute mode using one of two methods, depending on the
WAKE bit in the USART_CR1 register:
• Idle Line detection if the WAKE bit is reset,
•
Address Mark detection if the WAKE bit is set.
Idle line detection (WAKE=0)
The USART enters mute mode when the RWU bit is written to 1.
It wakes up when an Idle frame is detected. Then the RWU bit is cleared by hardware but
the IDLE bit is not set in the USART_SR register. RWU can also be written to 0 by software.
An example of mute mode behavior using idle line detection is given in
RX
RWU
RWU written to 1
Address mark detection (WAKE=1)
In this mode, bytes are recognized as addresses if their MSB is a '1' else they are
considered as data. In an address byte, the address of the targeted receiver is put on the 4
LSB. This 4-bit word is compared by the receiver with its own address which is programmed
in the ADD bits in the USART_CR2 register.
The USART enters mute mode when an address character is received which does not
match its programmed address. In this case, the RWU bit is set by hardware. The RXNE
flag is not set for this address byte and no interrupt nor DMA request is issued as the
USART would have entered mute mode.
It exits from mute mode when an address character is received which matches the
programmed address. Then the RWU bit is cleared and subsequent bytes are received
normally. The RXNE bit is set for the address character since the RWU bit has been
cleared.
The RWU bit can be written to as 0 or 1 when the receiver buffer contains no data (RXNE=0
in the USART_SR register). Otherwise the write attempt is ignored.
An example of mute mode behavior using address mark detection is given in
Universal synchronous asynchronous receiver transmitter (USART)

Figure 284. Mute mode using Idle line detection

Data 1 Data 2 Data 3
Mute Mode
DocID13902 Rev 15
Data 4 IDLE
Idle frame detected
Figure 284.
RXNE RXNE
Data 5 Data 6
Normal Mode
Figure 285.
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