The UART1 DTR and RI pins let the host MCU and nRF93M1 sleep and wake independently, with no data loss and no additional GPIO.
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DTR is the host wake-up signal. Asserting DTR brings the module out of power-saving sleep so the host can transmit.
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RI is the module's data-ready signal. nRF93M1 asserts RI when it has data for the host, and de-asserts it once the module is ready to receive data from the host. RI can therefore serve as the host MCU wake-up source, allowing the host to sleep during periods of no traffic.
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nRF93M1 buffers incoming network data while the host wakes, so no data is lost even when the host wakes from a deep sleep state of its own.
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With hardware flow control, the host observes its CTS pin, driven by nRF93M1 UART1 RTS, to know when the module is ready to receive. A pull-up on the host CTS pin is required. Without hardware flow control, the host monitors RI, or applies a timeout of at least the module wake latency between asserting DTR and its first transmit.