Atmel SAM4S Series, Preliminary Data Sheet

Page: 750 / 1163

750
11100B–ATARM–31-Jul-12
SAM4S Series [Preliminary]
US_THR. TXEMPTY remains low until the timeguard transmission is completed as the time-
guard is part of the current character being transmitted.
Figure 34-23. Timeguard Operations
Table 34-10 indicates the maximum length of a timeguard period that the transmitter can handle
in relation to the function of the Baud Rate.
34.7.3.11 Receiver Time-out
The Receiver Time-out provides support in handling variable-length frames. This feature detects
an idle condition on the RXD line. When a time-out is detected, the bit TIMEOUT in the Channel
Status Register (US_CSR) rises and can generate an interrupt, thus indicating to the driver an
end of frame.
The time-out delay period (during which the receiver waits for a new character) is programmed
in the TO field of the Receiver Time-out Register (US_RTOR). If the TO field is programmed
to 0, the Receiver Time-out is disabled and no time-out is detected. The TIMEOUT bit in
US_CSR remains to 0. Otherwise, the receiver loads a 16-bit counter with the value pro-
grammed 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 the Status Register rises.
Then, the user can either:
D0 D1 D2 D3 D4 D5 D6 D7
TXD
Start
Bit
Parity
Bit
Stop
Bit
Baud Rate
Clock
Start
Bit
TG = 4
Write
US_THR
D0 D1 D2 D3 D4 D5 D6 D7
Parity
Bit
Stop
Bit
TXRDY
TXEMPTY
TG = 4
Table 34-10. Maximum Timeguard Length Depending on Baud Rate
Baud Rate Bit time Timeguard
Bit/sec µs ms
1 200 833 212.50
9 600 104 26.56
14400 69.4 17.71
19200 52.1 13.28
28800 34.7 8.85
33400 29.9 7.63
56000 17.9 4.55
57600 17.4 4.43
115200 8.7 2.21