L9679P datasheet(172/272 Pages) STMICROELECTRONICS

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Remote sensor interface

L9679P

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DocID029275 Rev 1

9.1

PSI5 mode

All channels are compliant to the PSI-5 v1.3 specification as described below:



Two-wire current interface



Manchester coded digital data transmission



High data transmission speeds of 125 kbps and 189 kbps



Variable data word length (8 & 10 bit only)



1-bit parity



Synchronous operating mode with 3 time slots

An example of the data format for one possible PSI-5 protocol configuration is shown below.

Data size and the error checking may vary, but the presence of 2 sync start bits (referenced

below as sync bits) and 2 TGap time is consistent regardless.

Figure 39. PSI-5 remote sensor protocol (10-bit, 1-bit parity

9.1.1

Functional description

The Remote Sensor Interface block provides a hardware connection between the

microcontroller and up to twelve remote sensors (maximum three per channel). Each

channel is independent on the others, and is not influenced by possible fault conditions

occurring on other channels, such as short circuits to ground or to vehicle battery. Each

channel is supplied by a current limited DC voltage derived from SATBUCK, and monitors

the current sunk from its supply in order to extract encoded data. The remote sensor

modulates the current draw to transmit Manchester-encoded data back to the receiver. The

current level detection threshold for all channels is internally computed by the IC in order to

adapt the signal level to the sensors quiescent current.

All channels can be enabled or disabled independently via SPI commands. The operational

status of all channels can also be read via SPI command. All channels support individual

selective sync-pulse control to allow communication back to the remote sensor via sync-

pulse voltage modulation as described in the PSI5 v1.3 specification.

The message bits are encoded using a Manchester format, in which logic values are

determined by a current transition in the middle of the bit time. When configured for PIS5

sensors each interface supports Manchester 2 encoding as shown in Figure 40.

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