app: Change CTS pull-down to pull-up#219
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Seem to work OK.
I even verified against Linux host to leave FC pins floating:
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Also the nrf54L host is able to connect to network when CTS is floating on nRF91 side. |
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Previously CTS was pulled up, this prevented hosts without hardware flow control from using the default Serial Modem build. Changing CTS to pull-down allows Serial Modem to send even when the CTS and RTS pins float. This relies in DTR as main mechanism for UART control. The host must first enable its own UART before it enables Serial Modem UART with DTR. - With hardware flow control, this means that host drives it's RTS pin, so there is no difference in operation. Host should also have a pull-up for it's CTS pin, so when SM starts driving it's RTS, the host knows that SM is ready to receive. - Without hardware flow control, the Serial Modem is able to send (TX) to host. However, the timing with DTR and when SM is able to receive needs to be taken into account as host cannot observe it's CTS. Instead host must monitor the RI signal, which is de-asserted when SM UART is ready. Or alternatively, have a sufficient timeout between host asserting DTR and host's first TX operation. Important: It is highly recommended to use hardware flow control with Serial Modem. Signed-off-by: Markus Lassila <markus.lassila@nordicsemi.no> Co-authored-by: Divya S Pillai <91891495+divipillai@users.noreply.github.com>
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Previously CTS was pulled up, this prevented hosts without
hardware flow control from using the default Serial Modem build.
Changing CTS to pull-down allows Serial Modem to send even
when the CTS and RTS pins float.
This relies in DTR as main mechanism for UART control. The host
must first enable its own UART before it enables Serial Modem
UART with DTR.
With hardware flow control, this means that host drives it's
RTS pin, so there is no difference in operation.
Host should also have a pull-up for it's CTS pin, so when SM
starts driving it's RTS, the host knows that SM is ready to
receive.
Without hardware flow control, the Serial Modem is able to
send (TX) to host. However, the timing with DTR needs to be
taken into account as host cannot observe it's CTS.
Instead host must monitor the RI signal, which is de-asserted
when SM UART is ready. Or alternatively, have a sufficient
timeout between asserting DTR and first TX operation.
Important: It is highly recommended to use hardware flow control
with Serial Modem.