Datasheet

SAM4E [DATASHEET]
Atmel-11157D-ATARM-SAM4E16-SAM4E8-Datasheet_12-Jun-14
914
38.7.7 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.
While operating in Modem mode, the USART behaves as though in Asynchronous mode and all the parameter
configurations are available.
Table 38-14 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,
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 38-14. 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