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Partitioning example continued: SoC-Based Modem.

Typical structure of the modem product today (using a SoC approach).

A modern implementation would integrate all of the RAM, ROM, ADC and DAC and processors on a single SoC.

The RS-232 remains off chip owing to 24 volt and negative supply voltages whereas the SoC itself may be run at 3.3 volts.

The NV store is a large capacity Flash ROM device with low-bandwidth serial connection. At system boot, the main code for both processors is copied from the Flash to the two on-chip RAMS by the small, mask-programmed booter. Keeping the firmware in Flash allows the modem to be upgraded to correct bugs or encompass new communications standards.

GPIO is used for all of the digital I/O, with the UART transmit and receive paths being set up as special modes of two of the GPIO connections.

23: (C) 2008-11, DJ Greaves, University of Cambridge, Computer Laboratory.