STGAP1S datasheet(48/67 Pages) STMICROELECTRONICS

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Programming manual

STGAP1S

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DocID027190 Rev 3

9.1.2

WriteReg command

The device register can be written through the WriteReg command when the device is set in

the configuration mode only (refer to Section 9.1.1), otherwise the write command is ignored

and the SPI_ERR flag is forced low.

The WriteReg command is followed by the data to be written into the target register. The

CRC code following the data is based on both command and data bytes. In this way, in case

of communication error, a data byte cannot be decoded as a command and vice-versa (refer

to Section : CRC protection on page 45).

9.1.3

ReadReg command

The registers of the device can be read anytime through the ReadReg command. After the

command is received and decoded by the device, the register value and the respective CRC

code is prepared for the transmission. The CRC polynomial used by the device during the

transmission is different from the one used by the host, but the CRC code is not inverted

before transmission (refer to Section : CRC protection).

The time required to obtain the reading result changes according to the side where the

The reading of a remote register (isolated side), if no communication error occurs between

the two sides of the device, is available in 30 µs.

After the read result is ready, the host microcontroller must send another command in order

to receive it. The time required to make the read result available depends on the register

type: remote registers need longer time because of the isolated interface communication.

Table 16. WriteReg command synopsis

Byte

123

To device

100A AAAA(1)

1. The command byte where AAAAA is the address of the target register.

CCCC CCCC(2)

2. The CRC byte of the command, if the CRC check is disabled this byte is ignored.

DDDD DDDD(3)

3. Data to be written into the target register.

KKKK KKKK(4)

4. The CRC byte of the command and data, if the CRC check is disabled this byte is ignored.

Table 17. ReadReg command synopsis

Byte

3(1)

1. Proper time have to be waited in order to allow the device to prepare the data.

To device

101A AAAA(2)

2. The command byte where AAAAA is the address of the target register.

CCCC CCCC(3)

3. The CRC byte of the command, if the CRC check is disabled this byte is ignored.

0000 0000

CCCC CCCC(4)

4. The CRC byte of the NOP command.

From device

0000 0000

DDDD DDDD(5)

5. Data read from the target register.

KKKK KKKK(6)

6. The CRC byte of the data.

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