L9779WD datasheet(112/170 Pages) STMICROELECTRONICS

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Functional description

L9779WD

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time window. When a monitoring cycle ends (the end of the fixed time window has been

reached) a new monitoring cycle is started automatically.

A correct response within the time window (at a response time > 0ms) decreases an

ERROR COUNTER by one. An incorrect response, a response outside the time window or

response time = 0ms leads to the incrementing of the ERROR COUNTER by one.

"within the time window" means that the end of writing the last answer byte - i.e.

RESP_BYTE0 - falls into the fixed time window mentioned above (see picture below).

Except the last answer byte, the previous answer bytes may also be written earlier than the

beginning of the time window.

The question sequence is deterministic. A question will be repeated until it is answered

correctly both in value and in time. Then the next question is placed in the sequence.

The ERROR COUNTER (EC) is a 3-bit counter. Various actions are activated depending on

the value of the counter.

The result of the comparison of the controller response and the calculated correct response,

as well as the next question, are available in the registers REQUHI/REQULO after receiving

the µC response (LSB of RESP_BYTE0) and can be read by the controller.

Monitoring cycle

Figure 74. Monitoring cycle diagram

Generating questions

The generation of the 4-bit question (REQU [3-0]) is realized with a 4-bit counter and a 4-bit

Markov chain. The 4-bit counter only changes into the next state during the sequencer-run

when the previous question has been answered correctly in value and in time.

The Markov chain changes into the next state on the 1111b -> 0000b transition of the 4-bit

counter if the previous question has been answered correctly in value and in time.

Neither the counter state nor the Markov chain states are changed by a sequencer-run

because of a write-access to the RESPTIME register or the expiration of the time window.

The 4-bit counter and Markov chain are set to 0000b when RST_UV is active.

The singularity of the Markov chain is 0000b. To leave the singularity (after power-up, error

state), the feedback path (M3 + M2 + M1 + M0) is realized. The "real" feedback logic of the

Markov chain is the XOR gate (M3 XOR M2).

The following diagram shows the 4-bit Markov chain.

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