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 tτ
(approximately 300 ns) will be ignored by the USART and no interrupt request
will be generated as shown in Figure 1412. See the device-specific
datasheet for parameters.
Figure 1412. Glitch Suppression, USART Receive Not Started
URXDx
URXS
tτ
When a glitch is longer than tτ, or a valid start bit occurs on URXDx, the USART
receive operation is started and a majority vote is taken as shown in
Figure 1413. 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 1413. Glitch Suppression, USART Activated
URXDx
URXS
tτ
Majority Vote Taken