L9300 datasheet(84/178 Pages) STMICROELECTRONICS

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Bidirectional mode

Micro must send a valid Answer inside the timing interval defined by the two SPI programmable parameters

T_Valid_Answ_Start and T_Valid_Answ_End. The timing window restarts after each Query received.

In case the Micro sends an Answer before T_Valid_Answ_Start or after T_Valid_Answ_End an error will be

generated.

In case the WD_TO_RST_EN is set:

If there is no Answer before T_Answ_TimeOut elapses a WD_RST is generated, the internal

WD_RST_Cnt_Value is incremented and the flag WD_RST_TO_Answ is set.

In case the WD_TO_RST_EN is not set:

If there is no Answer before T_Answ_TimeOut elapses, the error event counter WD_Cnt_Value is decreased

and the device starts to wait again for the Answer with the same timing procedure. The WD_FSM is on the “Wait

for answer after an Error” state, the status register WD_FSM_Status = “11”. When the Micro sends the answer to

the device (T_start_ANSW) the WD_REQ_TMR timer starts to count.

Micro must send a new seed request inside the timing interval defined by the two SPI programmable parameters

T_Valid_Req_Start and T_Valid_Req_End. The timing window restarts at each Answer received.

In case the Micro sends the request before T_Valid_Req_Start or after T_Valid_Req_End an error is generated.

In case the WD_TO_RST_EN is set:

If there is no request before T_Req_TimeOut elapses a WD_RST is generated, the internal WD_RST_Cnt_Value

is incremented and the flag WD_RST_TO_Req is set.

In case the WD_TO_RST_EN is not set:

If there is no request before T_ Req _TimeOut elapses, the error event counter WD_Cnt_Value is decreased and

the device starts to wait again for the request with the same timing procedure. The WD_FSM is on the “Wait for

query after an Error” state, the status register WD_FSM_Status = “11”. When the Micro sends the request to the

device, the WD_ANSW_TMR timer starts to count.

Monodirectional mode

Micro must send a valid Answer inside the timing interval defined by the two SPI programmable parameters

T_Valid_Answ_Start and T_Valid_Answ_End. The first timing window starts after the first Query received. The

timing window restarts at each Answer received.

In case the Micro sends an answer before T_Valid_Answ_Start or after T_Valid_Answ_End an error will be

generated.

If there is no Answer before T_Answ_TimeOut elapses the same procedure as for bidirectional mode

(reset/”Wait for answer after an Error” depending on the WD_TO_RST_EN setting)is performed.

Micro must send a new seed request inside the timing window between two answers.

If there is no request before T_Answ_TimeOut elapses the same procedure as for the bidirectional mode

(reset/”Wait for query after an Error” depending on the WD_TO_RST_EN setting) is performed.

14.1.2

Watchdog states evolution

ASIC starts the WD evolution state machine (WD_FSM) in IDLE mode where it is waiting for the first seed request

from micro through SPI.

In this way the starting period is completely under the control of the Micro allowing to safely concluding boot

procedure before starting the WD seed request/answer mechanism. During this period WD configuration registers

can be programmed. The first seed request acts as a WD state machine start. After this event the WD never

stops and WD configuration registers become locked. A safety mechanism based on a “un-lock 20 bits key”

prevents to modify the configuration registers while the Q/A algorithm is running. The unlock procedure is

described in the SPI register paragraph.

WD_CNT is a 4-bit counter used to collect Good and Bad answer furnished by the Micro as reaction of Seeds

sent.

L9300

Q&A Watchdog

DS12258 - Rev 5

page 84/178

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