SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The Write Byte and Write Word messages (Figure 27-5) consist of a target address, a command word, transmitted data bytes and an optional PEC byte. In automatic address acknowledge mode, the data bytes and optional PEC byte are acknowledged without firmware interaction. The acknowledgment of the command word is configured through the PMBTCR register. The firmware receives an End of Message interrupt in all cases except for Write Word with PEC message, reads the status register and finds the data ready indication bit set.
In the case of a Write Word with PEC byte message, the data ready interrupt is enabled after receiving 4 bytes (command byte, the 2 data bytes and the PEC byte). The firmware reads the data from the PMBRXBUF register and must write the PMBACK register to acknowledge back to the controller. The PMBus module holds SCL low until the firmware responds to the received data.
In all other cases, the EOM interrupt is received and data can be read from the PMBRXBUF register. The firmware is not required to send an acknowledgment back to the controller.
The Write Byte message looks exactly the same as the Send Byte, except the RD_BYTE_COUNT register contains a 3. The Write Word message has a RD_BYTE_COUNT of 4.