STPM01 datasheet(27/60 Pages) STMICROELECTRONICS

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STPM01

Theory of operation

Doc ID 10853 Rev 8

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the nominal frequency value of CLKOUT. Two nominal frequency ranges are expected, from

4.000 MHz to 4.194 MHz (MDIV = 0) or from 8.000 MHz to 8.192 MHz (MDIV = 1).

8.12.1

RC Startup procedure

To use the device with RC oscillator the configuration bit RC (see Table 16) must be set.

Since the default configuration is for a crystal oscillator, when a RC oscillator is used instead

and the device is supplied for the very first time it is not internally clocked and consequently

the DSP is inactive. In this condition it is not possible to set RC or any other configuration bit.

The following SPI procedure can be run in order to set the RC bit and provide the clock to

the device:

●

Set the mode signal BANK;

●

Perform a software reset;

●

Read the registers: BANK mode signal should be checked and the records should

show something (not 000000F0);

●

Set the mode signal RD;

●

Read the registers through SPI just to check that RD mode signal has been set;

●

Clear the mode signal BANK;

●

DO NOT perform a reading, and write configuration bit RC;

In this way the RC oscillator is started. If the registers are read again, it can be seen that RD

and RC bits are set, and BANK is cleared.

Once the RC startup procedure is complete, the device is clocked and active and it is

possible to permanently write the RC bit.

For details on mode signals refer to Chapter 8.20, for SPI operations refer to Chapter 8.21.

Figure 20.

Different oscillator circuits (a): with quartz; (b): internal oscillator; (c): with external

source

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