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Atmel ARM-Based Evaluation Kit for SAM4S16C, 32-Bit ARM® Cortex® Microcontroller ATSAM4S-WPIR-RD ATSAM4S-WPIR-RD Data Sheet

Product codes
ATSAM4S-WPIR-RD
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SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
776
with the value programmed in TO. This counter is decremented at each bit period and reloaded each time a new 
character is received. If the counter reaches 0, the TIMEOUT bit in US_CSR rises. Then, the user can either:
Stop the counter clock until a new character is received. This is performed by writing a one to the STTTO 
(Start Time-out) bit the US_CR. In this case, the idle state on RXD before a new character is received will not 
provide a time-out. This prevents having to handle an interrupt before a character is received and allows 
waiting for the next idle state on RXD after a frame is received.
Obtain an interrupt while no character is received. This is performed by writing a one to the RETTO (Reload 
and Start Time-out) bit in the US_CR. If RETTO is performed, the counter starts counting down immediately 
from the value TO. This enables generation of a periodic interrupt so that a user time-out can be handled, for 
example when no key is pressed on a keyboard.
If STTTO is performed, the counter clock is stopped until a first character is received. The idle state on RXD before 
the start of the frame does not provide a time-out. This prevents having to obtain a periodic interrupt and enables a 
wait of the end of frame when the idle state on RXD is detected.
If RETTO is performed, the counter starts counting down immediately from the value TO. This enables generation 
of a periodic interrupt so that a user time-out can be handled, for example when no key is pressed on a keyboard. 
 shows the block diagram of the Receiver Time-out feature.
Figure 36-24. Receiver Time-out Block Diagram 
 gives the maximum time-out period for some standard baud rates. 
Table 36-11.
Maximum Time-out Period
Baud Rate (Bit/s)
Bit Time (µs)
Time-out (ms)
600
1,667
109,225
1,200
833
54,613
2,400
417
27,306
4,800
208
13,653
9,600
104
6,827
14,400
69
4,551
19,200
52
3,413
28,800
35
2,276
38,400
26
1,704
56,000
18
1,170
57,600
17
1,138
200,000
5
328
16-bit Time-out 
Counter
0
TO
TIMEOUT
Baud Rate 
Clock
=
Character
Received
RETTO
Load
Clock
16-bit 
Value
STTTO
D
Q
1
Clear