L9663 datasheet(30/106 Pages) STMICROELECTRONICS

30 / 106 page

Satellite interface

L9663

30/106

DS11401 Rev 6

for two valid start bits and so a new incoming frame can be stored without error in the new

timeslot.

In the simple configuration, the last valid message which ends in a timeslot is stored in the

buffer of the slot (so if a frame is currently stored in a timeslot and an incoming frame ends

in this timeslot, the old data are overwritten). In this mode slot error is never set.

It is also possible to disable the time slot monitoring and in this case, no timing check is

done: the first frame is assigned to the first buffer, the second to the second, and so on. This

means that the buffer index is incremented every time a frame is received both valid and

invalid (Manchester communication error).

After reset, the default mode for the time slot monitoring is "monitoring disabled".

3.3.2

Sensor data buffer

To avoid loss of data, a data buffer for each PSI5 transceiver is necessary. While the data

buffer is being read by SPI, at the beginning of the sensor data transfer the data register is

cleared and a new data frame can be accepted.

The incoming PSI5 sensor data, together with CRC and SID/GBIT (if selected) are written

into a receive buffer, which is large enough to hold the data of one sync pulse cycle (i.e. up

to six sensors). In order to avoid data-mixing between different cycle times the data must be

fetched by the µC before the next transmission cycle starts.

The figure below shows how sensor buffers are updated in synchronous mode.

At t0 the buffers contain no data; then a sync pulse is sent and data are received and stored

in each register during the cycle time; so at t1/t2 the buffers contain sensors data of the

current cycle time.

Figure 16. Sensor buffer in synchronous mode diagram

Table 5. Time (t0-t2) vs SensorData

Time/Sensor

SensorData1

Buffer Empty

D11

D12

SensorData2

Buffer Empty

D21

D22

SensorData3

Buffer Empty

D31

D32

SensorData4

Buffer Empty

D41

D42

0 V

sensor data

PSIx

t2 t

GAPG2710151533PS

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