Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Reset Strapping General Considerations

AN93

6.Set non-default frequency values—Ring.

7.Set non-default filter parameters.

8.Set non-default S-register values.

The modem is now ready to detect rings, answer another modem, call, or dial out to a remote modem. Some key default settings for the modem after reset or powerup include the following:

V.92 and fall-backs enabled (Si2494/93)

V.90 and fall-backs enabled (Si2457)

V.34 and fall-backs enabled (Si2439/34)

V.32bis and fall-backs enabled (Si2415)

V.22bis and fall-backs enabled (Si2404)

V.42/42bis enabled

+++ escape sequence enabled

Answer-on-ring is disabled

Speaker off

DTE echo enabled

Verbal result codes enabled

CTS only enabled

FCC (US) DAA and call progress settings

2.1.2. Reset Strapping: General Considerations

The different options available in the Si24xx ISOmodem family are selected by means of 10 kΩ pulldown resistors placed at certain pins. During power-on or pin reset, the ISOmodem’s signal pins are read and the option resistors are taken into account to determine the required configuration. After reset, the ISOmodem assumes the functionality selected by the corresponding combination of pulldown resistors.

Below is a summary of reset-strap options. Not all options are available on all part number or packages. Refer to Table 4, “ISOmodem Capabilities,” on page 10 for details.

Host interface: UART, parallel or SPI

Input clock frequency: 32 kHz, 4.9152 MHz or 27 MHz

Autobaud mode or fixed-rate UART communication (when UART interface is selected). Disabling the autobaud feature at reset sets the rate to 19,200 baud.

EEPROM interface

Three-wire EEPROM or four-wire EEPROM when EEPROM interface is selected

Refer to "2.6. EEPROM Interface (24-Pin TSSOP and 38-Pin QFN Only)" on page 31 for more details on the various ISOmodem EEPROM options.

The next few sections describe the various reset options that must be selected for each package. In all the tables, the following conventions apply:

0 means a 10 kΩ pulldown resistor to ground.

1 means the pin is left open. If a pin is left open, the internal pullup resistor is normally sufficient as long as the pin is not driven externally during reset. If there is noise or special power-sequencing situations, then an external pullup resistor may be needed.

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