SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The Block Read (Figure 1-1) protocol is similar to a Read Word in structure, except that there are more than 2 data bytes in the message. Following the receipt of the repeated target address, a data ready and data request interrupt is generated by the PMBus module. The command byte received from the controller can be found in bits 7-0 of the PMBRXBUF register. The SCL line is held low until the firmware programs data bytes into the PMBTXBUF register. The firmware is required to load the block length into bits 7-0 of the PMBTXBUF register during the initial programming of the register. After 4 bytes have been transmitted, the module issues a data request interrupt and holds SCL low again until the firmware has programmed additional data into the PMBTXBUF register.
Block read starts the same as Read Word or Read Byte, but TX_COUNT is loaded with a 4 the first time, and TX_PEC is not set. Instead of waiting for an EOM after the first transmission, the firmware instead waits for a Data Request, indicating that the controller is ready for more data. Until the last 4 or less bytes, the firmware simply writes a 4 to TX_COUNT and then writes the 4 bytes to PMBTXBUF. TX_PEC is left cleared. Then when the last 4 or fewer bytes are to be transmitted, the firmware writes out the appropriate byte count, sets the TX_PEC bit, and writes the data to PMBTXBUF. The PMBus module writes out the data, followed by the PEC, and then the EOM bit is set when the controller NACKs the PEC.