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
775
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
The duration of the idle state is programmed in the TG field of the Transmitter Timeguard register (US_TTGR).
When this field is written to zero no timeguard is generated. Otherwise, the transmitter holds a high level on TXD
after each transmitted byte during the number of bit periods programmed in TG in addition to the number of stop
bits.
As illustrated in
As illustrated in
, the behavior of TXRDY and TXEMPTY status bits is modified by the programming of
a timeguard. TXRDY rises only when the start bit of the next character is sent, and thus remains to 0 during the
timeguard transmission if a character has been written in US_THR. TXEMPTY remains low until the timeguard
transmission is completed as the timeguard is part of the current character being transmitted.
Figure 36-23. Timeguard Operations
indicates the maximum length of a timeguard period that the transmitter can handle in relation to the
function of the baud rate.
36.7.3.11Receiver 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 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 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 written to 0, the Receiver Time-out is disabled and no
time-out is detected. The TIMEOUT bit in the US_CSR remains at 0. Otherwise, the receiver loads a 16-bit counter
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 36-10.
Maximum Timeguard Length Depending on Baud Rate
Baud Rate (Bit/s)
Bit Time (µs)
Timeguard (ms)
1,200
833
212.50
9,600
104
26.56
14,400 69
.4
17.71
19,200
52.1
13.28
28,800
34.7
8.85
38,400
26
6.63
56,000
17.9
4.55
57,600
17.4
4.43
115,200
8.7
2.21