I have been taking a careful look at this reference design, my question is about the circuit included in file tidm_02010_ac_relay.SchDoc for the COM serial commnications used in this design, since the hardware seems to be full-duplex (there a re no signals to selectively activate SYS_TX output or SYS_RX input, as needed for half-duplex operation). I fail to grasp the logic, because the COM net needs to have a supply voltage for this circuit to operate, and even then I fail to understand how the SYS_RX net is going to get any signal from the COM net. It is easy to understand that SYS_TX pin will be able to generate a signal in the COM_RCQ net.
I am tempted to change this serial communications circuit for an isolated half-duplex interface using TI´s ISO14xx isolated RS485 transceivers, but for this to be possible, I would need to find at least a free output pin in the TMS320F280025CPMSR MCU, two free pins being ideal. I would like to find at least one, ideally two pins to be used as GPIO for controlling the ISO14xx half-duplex data flow.
One option at this time would be to use one of TI´s full-duplex isolated RS485 interfaces, the downside being that a full-duplex interface would require 4 transmit wires for outside-inside communications, increasing cost and complexity.
What I want to achieve is using TIDM-020210 as an air conditioning outside driver unit, to be paired with a yet to be selected/designed air conditioning inside driver unit.
I have been looking at all the technical details provided by TI for this reference design, and it seems something I could be able to build from your design.