ST7263BEx datasheet(88/186 Pages) STMICROELECTRONICS

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On-chip peripherals

ST7263Bxx

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Doc ID 7516 Rev 8

clock occurs just before the pin value changes, the samples would then be out of sync by

~4 µs. This means the entire bit length must be at least 40 µs (36 µs for the 10th sample + 4

µs for synchronization with the internal sampling clock).

Clock deviation causes

The causes which contribute to the total deviation are:

●

DTRA: Deviation due to transmitter error (Local oscillator error of the transmitter or the

transmitter is transmitting at a different baud rate).

●

DQUANT: Error due to the baud rate quantisation of the receiver.

●

DREC: Deviation of the local oscillator of the receiver: This deviation can occur during

the reception of one complete SCI message assuming that the deviation has been

compensated at the beginning of the message.

●

DTCL: Deviation due to the transmission line (generally due to the transceivers)

All the deviations of the system should be added and compared to the SCI clock tolerance:

DTRA + DQUANT + DREC + DTCL < 3.75%

Noise error causes

See also description of Noise error in Section .

Start bit

The noise flag (NF) is set during start bit reception if one of the following conditions occurs:

A valid falling edge is not detected. A falling edge is considered to be valid if the 3

consecutive samples before the falling edge occurs are detected as '1' and, after the

falling edge occurs, during the sampling of the 16 samples, if one of the samples

numbered 3, 5 or 7 is detected as a “1”.

During sampling of the 16 samples, if one of the samples numbered 8, 9 or 10 is

detected as a “1”.

Therefore, a valid Start Bit must satisfy both the above conditions to prevent the Noise Flag

getting set.

Data bits

The noise flag (NF) is set during normal data bit reception if the following condition occurs:

●

During the sampling of 16 samples, if all three samples numbered 8, 9 and10 are not

the same. The majority of the 8th, 9th and 10th samples is considered as the bit value.

Therefore, a valid Data Bit must have samples 8, 9 and 10 at the same value to prevent the

Noise Flag getting set.

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