Process Call W/O Pec Byte; Process Call With Pec Byte - Texas Instruments UCD3138 Technical Reference Manual

Master Mode Operation Reference
10.7.6 Process Call
S Device Addr
The Process Call protocol consists of a Write Word message, followed by a Read Word message, without
a stop condition between the two messages. A PEC byte can be appended to the read data from the slave
as an option to the message protocol. The Master Control Register includes a PRC_CALL bit, which
enables the transmission of a Process Call message onto the PMBus. The PMBus Interface will
automatically generate a repeated start condition and initiate the Read Word portion of the message when
the process call bit is enabled.
To complete the Write Word portion of the Process Call, the Transmit Data Register is loaded with the
command byte in Bits 7-0 and the data bytes are loaded into Bits 23-8 of the register.
After programming the Master Control Register, the PMBus Interface initiates the Process Call Message
on the PMBus. The firmware can wait for an End of Message interrupt from the interface to determine the
validity of the message. Upon the receipt of the EOM, the Status Register should indicate the receipt of 2
bytes from the Read Word portion of the Process Call message and the status of the Slave
acknowledgement of the transmit data. If PEC processing is enabled, the PEC_VAL bit within the Status
Register indicates the accuracy of the PEC byte received from the Slave during the Read Word part of the
message.
The PRC_CALL bit within the Master Control Register should be disabled on the next message not of the
Process Call protocol. Please note that any write to the Master Control Register initiates a message, so
reconfiguration of the Master is not recommended until the firmware requires a new message to be
transmitted on the PMBus.
376
PMBus Interface/I2C Interface
Figure 10-35. Process Call w/o PEC Byte
Wr A Command A Byte #0
Byte #0 A Byte #1
Figure 10-36. Process Call with PEC Byte
Copyright © 2016, Texas Instruments Incorporated
A Byte #1 A Sr Device Addr
A PEC NA P
SNIU028A – February 2016 – Revised April 2016
www.ti.com
Rd A
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