ST10F276 datasheet(63/229 Pages) STMICROELECTRONICS

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ST10F276

Bootstrap loader

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5.4.6

Computing the baud rate error

Considering the following conditions, a computation of the error is given as an example.

●

CPU frequency: 20 MHz

●

Target Bit Rate: 1 Mbit/s

In these conditions, the content of PT0 timer for 29 bits should be:

Therefore:

574 < [PT0] < 586

This gives:

BRP = 0

tq = 100 ns

Computation of 1 + Tseg1 + Tseg2: Considering the equation:

[PT0] = 58 x (1 + BRP) x (1 + Tseg1 + Tseg2)

Thus:

In the algorithm, a rounding up to the superior value is made if the remainder of the division

is greater than half of the divisor. This would have been the case if the PT0 content was 574.

Thus, in this example the result is 1 + Tseg1 + Tseg2 = 10, giving a bit time of exactly 1

µs

=> no error in bit rate.

Note:

In most cases (24 MHz, 32 MHz, 40 MHz of CPU frequency and 125, 250, 500 or 1Mb/s of

bit rate), there is no error. Nevertheless, it is better to check for an error with the real

application parameters.

The content of the bit timing register is: 0x1640. This gives a sample point at 80%.

Note:

The (Re)Synchronization Jump Width is fixed to 2 time quanta.

5.4.7

Bootstrap via CAN

After the bootstrap phase, the ST10F276 CAN module is configured as follows:

●

The pin P4.6 is configured as output (the latch value is ‘1’ = recessive) to assume

CAN1_TxD function.

●

The MO2 is configured to output the acknowledge of the bootstrap with the standard

identifier E6h, a DLC of 3 and Data0 = D5h, Data1 and 2 = IDCHIP.

●

The MO1 is configured to receive messages with the standard identifier 5h. Its

acceptance mask is set to ensure that all bits match. The DLC received is not checked:

The ST10 expects only 1 byte of data at a time.

No other message is sent by the ST10F276 after the acknowledge.

Note:

The CAN boot waits for 128 bytes of data instead of 32 bytes (see UART boot). This is done

to allow the User to reconfigure the CAN bit rate as soon as possible.

PT0

[]

29 Fcpu

BitRate

---------------------------

110

-----------------------------

580

574

---------- Tseg1 Tseg2 586

----------10

≤

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