Bootloader description

AN2792

6/12

2.2

Peripheral settings

This section describes the hardware setting of the STM8A USART communication

peripheral.

Note:

LINUART, SPI and CAN peripherals may also be used during bootloading, however, only

one peripheral is enabled at a time; all others are disabled.

The USART settings are:

●

Data frame: 1 start bit, 8 data bit, 1 parity bit even, 1 stop bit

●

Baud rate: The baud rate is autodetected by the bootloader. When the user sends

synchronization byte, 7Fh, the bootloader automatically detects the baud rate and sets

the USART to the same baud rate. Maximum baud rate = 1 Mbps; minimum baud rate

= 4800 bps.

Mandatory: To perform the automatic speed detection, the RX line (PA4) has to be stable in

the application board.

Note:

The USART peripheral is accessible via pins PA4 (RX) and PA5 (TX).

Table 1.

1.

After interface initialization, a write protection test is performed to avoid non-authorised reading of the

Flash program memory/data EEPROM,

Checks

Program memory

location 8000h

Bootloader

check

opt_byte 487Eh

Bootloader

check

opt_byteN

487Fh

Actual Flash program

memory status

-> Flash action

XXh! = (82h or ACh)

XXh

XXh

Flash program memory

virgin

-> jump to bootloader

XXh = (82h or ACh)

55h

AAh

Flash program memory

already written

-> jump to bootloader

XXh = (82h or ACh)

XXh! = 55h

XXh! = AAh

Flash program memory

already written

-> jump to Flash program

memory reset

Table 2.

Serial interfaces associated with STM8A devices

Device

Serial interface

128 Kbyte, 96 Kbyte, 64 Kbyte, 48 Kbyte

USART, LINUART, CAN

32 Kbyte, 16 Kbyte

LINUART, SPI