RM0453 Rev 2 1177/1454
RM0453 Universal synchronous/asynchronous receiver transmitter (USART/UART)
1257
Bits 31:24 ADD[7:0]: Address of the USART node
These bits give the address of the USART node in Mute mode or a character code to be recognized
in low-power or Run mode:
– In Mute mode: they are used in multiprocessor communication to wakeup from Mute mode
with 4-bit/7-bit address mark detection. The MSB of the character sent by the transmitter
should be equal to 1. In 4-bit address mark detection, only ADD[3:0] bits are used.
– In low-power mode: they are used for wake up from low-power mode on character match.
When WUS[1:0] is programmed to 0b00 (WUF active on address match), the wakeup from
low-power mode is performed when the received character corresponds to the character
programmed through ADD[6:0] or ADD[3:0] bitfield (depending on ADDM7 bit), and WUF
interrupt is enabled by setting WUFIE bit. The MSB of the character sent by transmitter
should be equal to 1.
– In Run mode with Mute mode inactive (for example, end-of-block detection in ModBus
protocol): the whole received character (8 bits) is compared to ADD[7:0] value and CMF
flag is set on match. An interrupt is generated if the CMIE bit is set.
These bits can only be written when the reception is disabled (RE = 0) or when the USART is
disabled (UE = 0).
Bit 23 RTOEN: Receiver timeout enable
This bit is set and cleared by software.
0: Receiver timeout feature disabled.
1: Receiver timeout feature enabled.
When this feature is enabled, the RTOF flag in the USART_ISR register is set if the RX line is idle
(no reception) for the duration programmed in the RTOR (receiver timeout register).
Note: If the USART does not support the Receiver timeout feature, this bit is reserved and must be
kept at reset value. Refer to Section 35.4: USART implementation on page 1120.
Bits 22:21 ABRMOD[1:0]: Auto baud rate mode
These bits are set and cleared by software.
00: Measurement of the start bit is used to detect the baud rate.
01: Falling edge to falling edge measurement (the received frame must start with a single bit = 1
and Frame = Start10xxxxxx)
10: 0x7F frame detection.
11: 0x55 frame detection
This bitfield can only be written when ABREN = 0 or the USART is disabled (UE = 0).
Note: If DATAINV = 1 and/or MSBFIRST = 1 the patterns must be the same on the line, for example
0xAA for MSBFIRST)
If the USART does not support the auto baud rate feature, this bit is reserved and must be kept
at reset value. Refer to Section 35.4: USART implementation on page 1120.
Bit 20 ABREN: Auto baud rate enable
This bit is set and cleared by software.
0: Auto baud rate detection is disabled.
1: Auto baud rate detection is enabled.
Note: If the USART does not support the auto baud rate feature, this bit is reserved and must be kept
at reset value. Refer to Section 35.4: USART implementation on page 1120.
Bit 19 MSBFIRST: Most significant bit first
This bit is set and cleared by software.
0: data is transmitted/received with data bit 0 first, following the start bit.
1: data is transmitted/received with the MSB (bit 7/8) first, following the start bit.
This bitfield can only be written when the USART is disabled (UE = 0).
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