You should be able to use USART1 on D28and D29 (see pinout )
D28
D29
Then most of the effort is already done for SIM900 and SIM800.
@Jean-Philippe_Rey started
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You should be able to use USART1 on
D28
andD29
(see pinout )Then most of the effort is already done for SIM900 and SIM800.