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USART Operation: UART Mode
14-20 USART Peripheral Interface, UART Mode
Receive-Start Edge Detect Conditions
When URXSE = 1, glitch suppression prevents the USART from being
accidentally started. Any low-level on URXDx shorter than the deglitch time t
τ
(approximately 300 ns) will be ignored by the USART and no interrupt request
will be generated as shown in Figure 14−12. See the device-specific
datasheet for parameters.
Figure 14−12. Glitch Suppression, USART Receive Not Started
URXDx
URXS
t
τ
When a glitch is longer than t
τ,
or a valid start bit occurs on URXDx, the USART
receive operation is started and a majority vote is taken as shown in
Figure 14−13. If the majority vote fails to detect a start bit the USART halts
character reception.
If character reception is halted, an active BRCLK is not necessary. A time-out
period longer than the character receive duration can be used by software to
indicate that a character was not received in the expected time and the
software can disable BRCLK.
Figure 14−13. Glitch Suppression, USART Activated
URXDx
URXS
t
τ
Majority Vote Taken