L9679E datasheet(82/127 Pages) STMICROELECTRONICS

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8.1

PSI-5 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- and 10-bit only)

•

1-bit parity

•

Asynchronous operating mode with 3 stage input data buffers

•

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 21. PSI-5 remote sensor protocol (10-bit, 1-bit parity)

Data Transmission

Manchester Code

Transmission of 0x1E7

0x1E7 = 01 1110 0111b

frame duration

BIT

Gap

"0"

"1"

"0"

"1"

"0"

"1"

GADG0903181523PS

8.1.1

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 from the others, and is not influenced

by possible fault conditions occurring on other channels, such as shortcircuits to ground or to vehicle battery.

Each channel is supplied by a current limited DC voltage derived from VSAT pin, 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.

In case asynchronous mode is selected for one interface the sync pulse is not generated (sync pulse control bit is

don’t care).

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 22. Manchester bit encoding.

Figure 22. Manchester bit encoding

Logic '0'

Logic '1'

Manchester-2

PSI5

Bit time

‘0’

‘1’

‘0’

‘1’

Current

Start bits = ‘00’

GADG0903181529PS

L9679E

Remote sensor interface

DS12485 - Rev 8

page 82/127

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