I just finished designing a board with two UCD9240 parts. I did not thoroughly study the UCD9240 datasheet and falsely assumed that I could simply control unused pins, configured as GPIO, through the PMBus. Unfortunately the board is finished and I'm looking for a workaround.
I have an FPGA that is the I2C master of the bus. I would like the FPGA to be able to write some PMBus commands to the UCD9240 in order to actively drive the DPWM-1B, DPWM-2B, SRE-1B, and SRE-2B pins with an arbitrary state. I understand it is not possible to simply write to a firmware register to change the state of the GPIO. I was wondering if it is theoretically possible to reprogram these GPIO on-the-fly? Suppose I configure one of these pins to drive active-high as long as Rail #X is within it's programmed limits, and then reprogram it to drive active-low instead?
I was planning to try this, but since I don't have much experience with the PMBus, I was hoping an expert could give me some advice before I spend a lot of time designing I2C command sequences.
It is possible to change the configuration of a GPIO pin with a PMBus command but GPIO functionality is a very low level process in the controller and requires that the device be in a non-converting state (no rails converting power) to be processed. I've never tried it but changing the active state of a pin defined as a GPO should force it to change its output assuming it will still function if not set to monitor a particular function. So if you can disable rail operation between chanaging the GPO states than it may work.