SI2439 datasheet(21/70 Pages) SILABS

21 / 70 page

Si2494/39

Rev. 1.0

4.8. Low-Power Modes

The Si2494/39 provides multiple low power modes. Using the S24 S-register, the Si2494/39 can be set to

automatically enter sleep mode after a pre-programmed time of inactivity with either the DTE or the remote

modem. The sleep mode is entered after (S24) seconds have passed since the last DTE activity, after the transmit

FIFO is empty, and after the last data are received from the remote modem.

Additionally, the Si2494/39 can be placed in wake-on-ring-mode using the command, AT&Z. In either mode, the

ISOmodem remains in the sleep state until one of the following occurs:



A 1-to-0 transition on TXD (UART mode).



A 1-to-0 transition on SS (SPI mode).



A 1-to-0 transition on CS (parallel mode).



An incoming ring is detected.



A parallel telephone is picked up.



Line polarity reversal

The Si2494/39 may also be placed in a complete powerdown mode. Once the Si2494/39 completely powers down,

it can only be powered back on via the RESET pin.

4.9. Data Compression

The modem can achieve DTE (host-to-ISOmodem) speeds greater than the maximum DCE (modem-to-modem)

speed through the use of a data compression protocol. The compression protocols available are the ITU-T V.44,

V.42bis, and MNP5 protocols. Data compression attempts to increase throughput by compressing the data before

actually sending it. Thus, the modem is able to transmit more data in a given period of time.

4.10. Error Correction

The Si2494/39 ISOmodem can employ error correction (reliable) protocols to ensure error-free delivery of

asynchronous data sent between the host and the remote end. The Si2494/39 supports V.42 and MNP2-4 error

correction protocols. V.42 (LAPM) is most commonly used and is enabled by default.

4.11. Wire Mode

Wire mode is used to communicate with standard non-error correcting modems. When optioned with \N3, the

Si2494/39 falls back to wire mode if it fails in an attempt to negotiate a V.42 link with the remote modem. Error

correction and data compression are not active in wire mode.

SI2439 Datasheet(PDF) 21 Page - Silicon Laboratories