ST10F296E datasheet(76/346 Pages) STMICROELECTRONICS

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The bootstrap loader

ST10F296E

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This process may go through several iterations or may directly execute the final application.

In all cases, the ST10F296E runs in BSL mode, i.e. with the watchdog timer disabled and

limited access to the internal Flash area. All code fetches from the internal IFlash area

(01’0000H...08’FFFFH) are redirected to the special Test-Flash. Data read operations

access the internal Flash of the ST10F296E, if any is available, but return undefined data on

ROM-less devices.

6.3.5

Choosing the baud rate for the BSL via UART

The calculation of the serial baud rate for ASC0 from the length of the first zero byte that is

received, allows the bootstrap loader of the ST10F296E to operate with a wide range of

baud rates. However, upper and lower limits have to be respected to insure proper data

transfer.

Equation 1

The ST10F296E uses Timer T6 to measure the length of the initial zero byte. The

quantization uncertainty of this measurement implies the first deviation from the real baud

rate. The next deviation is implied by the computation of the S0BRL reload value from the

timer contents. Equation 2 below shows the association:

Equation 2

Where:

For correct data transfer from the host to the ST10F296E, the maximum deviation between

the internal initialized baud rate for ASC0 and the real baud rate of the host should be below

2.5 %. The deviation (FB, in percent) between host baud rate and the ST10F296E baud rate

can be calculated via Equation 3:

Equation 3

where:

≤ 2.5 %

Note:

FB does not consider the tolerances of oscillators and other devices supporting the serial

communication.

This baud rate deviation is a nonlinear function depending on the CPU clock and the baud

rate of the host. The maxima of FB increases with the host baud rate due to the smaller

baud rate pre-scaler factors and the implied higher quantization error (see Figure 11).

ST10F296

CPU

SOBRL

()

⁄

SOBRL

–

() 72

⁄

CPU

Host

⁄

Contr

Host

–

() B

Contr

⁄

100

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