SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The Block Read protocol is similar to a Read Word in its structure, with the exception of reception of more than 2 data bytes from the Slave. The first data byte transmitted by the Slave represents the block length of the data being written by the slave. If PEC processing is enabled, the Slave appends a PEC byte to the end of the message.
To initiate a Block Read message on the PMBus, the Master Control Register is programmed with the block length in the Byte Count bits. This count excludes the command byte, any slave address and the block length bytes in the message. The command byte to be transmitted to the Slave is written into bits 7-0 of the Transmit Data Register prior to the programming of the Master Control Register.
After configuring the Master Control Register, the Block Read message is initiated on the PMBus. The interface interrupts the firmware upon receipt of 4 data bytes from the slave. If the block length is 3, the EOM interrupt will be received concurrently with the data ready interrupt. Otherwise, a data ready interrupt is asserted, indicating 4 bytes are ready for reading by the firmware. At the end of the message, less than 4 bytes may be stored in the Receive Data Register. The RX Byte Count bits in the Status Register indicate the number of bytes available in the final data transfer. The firmware may verify the received PEC upon detection of the End of Message interrupt.