L9678P datasheet(131/215 Pages) STMICROELECTRONICS

131 / 215 page

DS11626 Rev 9

131/216

L9678P, L9678P-S

Remote sensor interface

214

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

Data size may vary, but the presence of 2 sync start bits (referenced below as sync bits) and

TGap time is consistent regardless of the data size.

Figure 32. PSI-5 remote sensor protocol (10-bit, 1-bit parity)

7.1.1

Functional description - remote sensor modes

The Remote sensor Interface block provides a hardware connection between the

microcontroller and up to two remote sensors. Each channel is independent of the other,

and is not influenced by fault conditions, such as short circuits to ground or vehicle battery,

on the other channel. Each channel supplies an independently current limited DC voltage to

its remote sensor derived from VSUP, and monitors the current draw to extract encoded

data. The remote sensors modulate the current draw to transmit Manchester-encoded data

back to the receiver. The current level detection threshold for all channels is automatically

set by the integrated current adjust feature in order to adapt to the quiescent current draw of

the sensors.

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

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

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. The interface supports

Manchester 2 encoding as shown in Figure 33.

Figure 33. Manchester bit encoding

The received message data are stored in input data registers that are read out by the

microcontroller via the SPI interface. All bits of these registers are simultaneously updated

upon reception of the remote sensor message to prevent partial frame data from being

sampled via the SPI interface. After the data for a given channel is read via the SPI

GAPGPS01132

Data Transmission

Manchester Code

Transmission of 0x1E7

0x1E7 = 01 1110 0111b

frame duration

BIT

GAP

"0"

"1"

"0"

"1"

"0"

"1"

GAPGPS01133

Logic '0'

Logic '1'

Manchester-2

PSI5

Bit time

‘0’

‘1’

‘0’

‘1’

Current

Start bits = ’00’

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