Datasheet
905
SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
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.
Figure 38-24 shows the block diagram of the Receiver Time-out feature.
Figure 38-24. Receiver Time-out Block Diagram
Table 38-11 gives the maximum time-out period for some standard baud rates.
Table 38-11. 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
DQ
1
Clear