Apply the following settings:
- Set matching VDD on both boards (typically 1.8 V).
On the nRF9151 or nRF9151 SMA DK (Serial Modem):
- Disconnect VCOM0 so the UART0 data pins (P0.26/P0.27) are free for the external host link. Serial Modem uses the nRF91M1 pinout on UART0.
- Disconnect VCOM0 HWFC too. This is a separate switch from VCOM0 and, like it, defaults to Connected. Leaving it connected keeps the interface MCU on P0.14/P0.15 through 150 Ω series resistors, holding the modem's CTS deasserted so it never answers the host's init chat script.
- Leave VCOM1 and VCOM1 HWFC connected for modem logs (UART1, P0.28/P0.29). CI captures this port at 1000000 baud.
Host-specific settings are listed in each of the following sections.