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
785
SAM4S Series [DATASHEET]
Atmel-11100G-ATARM-SAM4S-Datasheet_27-May-14
36.7.7 Modem Mode
The USART features modem mode, which enables control of the signals: DTR (Data Terminal Ready), DSR (Data
Set Ready), RTS (Request to Send), CTS (Clear to Send), DCD (Data Carrier Detect) and RI (Ring Indicator).
While operating in modem mode, the USART behaves as a DTE (Data Terminal Equipment) as it drives DTR and
RTS and can detect level change on DSR, DCD, CTS and RI.
Setting the USART in modem mode is performed by writing the USART_MODE field in US_MR to the value 0x3.
Setting the USART in modem mode is performed by writing the USART_MODE field in US_MR to the value 0x3.
While operating in modem mode, the USART behaves as though in asynchronous mode and all the parameter
configurations are available.
gives the correspondence of the USART signals with modem connection standards.
The control of the DTR output pin is performed by writing a one to the DTRDIS and DTREN bits respectively in
US_CR. The disable command forces the corresponding pin to its inactive level, i.e., high. The enable command
forces the corresponding pin to its active level, i.e., low. The RTS output pin is automatically controlled in this
mode.
The level changes are detected on the RI, DSR, DCD and CTS pins. If an input change is detected, the RIIC,
The level changes are detected on the RI, DSR, DCD and CTS pins. If an input change is detected, the RIIC,
DSRIC, DCDIC and CTSIC bits in US_CSR are set respectively and can trigger an interrupt. The status is
automatically cleared when US_CSR is read. Furthermore, the CTS automatically disables the transmitter when it
is detected at its inactive state. If a character is being transmitted when the CTS rises, the character transmission
is completed before the transmitter is actually disabled.
Table 36-14.
Circuit References
USART Pin
V24
CCITT
Direction
TXD
2
103
From terminal to modem
RTS
4
105
From terminal to modem
DTR
20
108.2
From terminal to modem
RXD
3
104
From modem to terminal
CTS
5
106
From terminal to modem
DSR
6
107
From terminal to modem
DCD
8
109
From terminal to modem
RI
22
125
From terminal to modem