SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
Since the read commands only provide a command code, it is first necessary to provide an address to read from. The read address is set up through a PMBus Write Block message with a command byte of 0xFD. Starting with the device address of 0xB (with R/W bit set low), the Configure Read Address message contains a command byte of 0xFD, followed by 5 data bytes and a PEC byte. The first data byte represents the block size for a PMBus Block Write message, which will always contain a value of 0x4 for this message type. The remaining bytes represent the read address, starting with the most significant byte in the second data byte and the least significant byte in the fifth data byte. The PEC byte completes the message. The PMBus Master provides all 8 bytes of the message.
Note that the device address occupies bits 7 to 1 of the second byte, and the R/W bit occupies bit 0. So with a device address of 0xB and the R/W bit = 0, the byte value will be 0x16. See Section 10.11.1 for more details.
Also note that in the following illustrations, grey boxes indicate communications from master to slave (UCD) and white boxes communications from UCD to master.
Start | Device Address & R/W (0x16) | Command Byte (0xFD) | Block Size (0x04) | Read Address[31:24] |
Read Address[24:16] | Read Address[15:8] | Read Address[7:0] | PEC | Stop |