UM0470 datasheet(9/37 Pages) STMICROELECTRONICS

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UM0470

Single wire interface module (SWIM)

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3.3.1

High speed bit format

1 bit is generated with ten HSI oscillator pulses.

The bit format is:

- 2 pulses at ‘0’ followed by 8 pulses at ‘1’ for ‘1’ value.

- 8 pulses at ‘0’ followed by 2 pulses at ‘1’ for ‘0’ value.

When the SWIM module receives a data packet, it will decode:

- ‘1’ when the number of consecutive samples at ‘0’ is less or equal to 4.

- ‘0’ when the number of consecutive samples at ‘0’ is greater or equal to 5.

Figure 6.

High speed bit format

3.3.2

Low speed bit format

1 bit is generated with twenty-two HSI oscillator pulses.

The bit format is:

- 2 pulses at ‘0’ followed by 20 pulses at ‘1’ for ‘1’ value.

- 20 pulses at ‘0’ followed by 2 pulses at ‘1’ for ‘0’ value.

When the SWIM module receives a data packet, it will decode:

- ‘1’ when the number of consecutive samples at ‘0’ is less or equal to 8.

- ‘0’ when the number of consecutive samples at ‘0’ is greater or equal to 9.

Figure 7.

Low speed bit format

<=> ‘1’

<=> ‘0’

<=> ‘1’

<=> ‘0’

UM0470 Datasheet(PDF) 9 Page - STMicroelectronics