SAM9G35_14 Datasheet, PDF (827/1293 Pages) ATMEL Corporation – ARM-based Embedded MPU

Then, the user can either:
 Stop the counter clock until a new character is received. This is performed by writing the Control Register (US_CR)
with the STTTO (Start Time-out) bit to 1. 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 US_CR with the RETTO (Reload
and Start Time-out) bit to 1. 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.
Figure 39-24 shows the block diagram of the Receiver Time-out feature.
Figure 39-24.Receiver Time-out Block Diagram
Baud Rate
TO
Clock
1
STTTO
Character
Received
RETTO
DQ
Clear
Clock
16-bit Time-out
Counter
Load
16-bit
Value
=
0
TIMEOUT
Table 39-11 gives the maximum time-out period for some standard baud rates.
Table 39-11. Maximum Time-out Period
Baud Rate
bit/sec
600
1 200
2 400
4 800
9 600
14400
19200
28800
33400
56000
57600
200000
Bit Time
µs
1 667
833
417
208
104
69
52
35
30
18
17
5
Time-out
ms
109 225
54 613
27 306
13 653
6 827
4 551
3 413
2 276
1 962
1 170
1 138
328
SAM9G35 [DATASHEET]
11053E–ATARM–10-Mar-2014
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