SNIU028D February 2016 – September 2020 UCD3138 , UCD3138064 , UCD3138064A , UCD3138128 , UCD3138A , UCD3138A64
The Write Byte and Write Word messages consist of a device address, a command byte, transmitted data bytes and an optional PEC byte. Write Byte messages include a single byte, while the Write Word messages support transmission of 2 bytes to the corresponding slave module. Similar to the Send Byte protocol, the Master Control Register is configured to send 1 or 2 bytes, the CMD_EN bit is set to enable command byte transmission and the optional PEC_EN bit is set.
With the command byte transmission enabled, the format of the Transmit Data Register differs from the Send Byte protocol. In Bits 7-0 of the Transmit Data Register, the firmware must program the command byte to be sent to the slave. The data byte(s) are programmed into bits 15-8 and bits 23-16.
After programming the Master Control Register, the PMBus Interface initiates a Write Byte/Word message on the PMBus. The firmware can wait for an End of Message interrupt from the interface to verify the accuracy of the message transmission. The Status Register indicates if the slave acknowledged the message properly.