S
Alert Response Addr
Rd
A
Device Addr
NA
P
Avoiding Clock Stretching
368
SNIU028A – February 2016 – Revised April 2016
Copyright © 2016, Texas Instruments Incorporated
PMBus Interface/I2C Interface
10.4.2 Alert Response
Figure 10-16. Alert Response
The UCD3138 PMBus interface provides an automated handling of the ALERT Response. To enable it,
set the ALERT_EN bit in PMBCTRL3. This will pull the ALERT pin low, and enable the ALERT response
from the hardware. If MAN_SLAVE_ACK is not set, the hardware will automatically acknowledge the
special ALERT address, and will automatically to the arbitration with the device address. If the UCD wins
the arbitration, it will automatically release the ALERT line and clear the ALERT_EN bit.
In manual address acknowledge mode (MAN_SLAVE_ACK is set), the firmware must read the received
address from the Receive Data Register and transmit the desired slave address back to the Master. The
firmware must check for LOST_ARB, and clear the ALERT_EN bit if the arbitration is won.