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I am working on integrating Sim900a on Rpi3B. As usual connecting to TX->Rx, Rx->Tx (GPIO14, GPIO15 in Rpi) - following diagram from this link: How do I connect GSM SIM 900A to a Raspberry Pi 3?

When I testing using Minicom 2.7x, it shows below error. My minicom setting using serial /dev/ttyS0 and baudrate 9600 (as baudrate 15200 got jammed the console and no response)

raspberrypi login:

raspberrypi login:

raspberrypi login:

raspberrypi login:

raspberrypi login:

raspberrypi login:

raspberrypi login:

ERROR

The error occurs even before typing AT command and it loop the error many times.

I tried to connect the Sim900A module to UART->USB converter, and connect to Windows 10 laptop, tested it using Putty, COM7 with baudrate 9600, It all works well.

Any solution?

Additional info on my Sim900a: Manufacture: Simcom Model:SIM900A S2-104V-Z094T

Mr Hery
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1 Answers1

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This seems to be a rather basic issue: your system is configured to provide a login shell (and possibly kernel boot messages) over the UART. You need to disable it in order to use the serial for your own purposes.

This can be done using sudo raspi-config (go to Advanced Functions - Serial and select "No" to disable the shell over the serial port), then reboot. Normally that's all that should be needed.

Alternatively disabling kernel boot messages can also be done by removing console=ttyAMA0,115200 (or something similar) from /boot/cmdline.txt (this one needs a reboot). Disabling the login shell can be done by running sudo systemctl stop getty@ttyAMA0 (this one is effective immediately, until a reboot). You can also disable it permanently with sudo systemctl disable serial-getty@ttyAMA0.service

Dmitry Grigoryev
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