After long hours to find right to solution to connect my Waveshare SIM7600, here are my settings that works :

• Keep yellow UART jumpers on B mode on SIM7600 card.
• Keep yellow jumper between 3V3 and VCCIO pins on the yellow jumpers.
  My card is an old card, on newer card you still have 3V3 with PWR pins and another jumper between D4 and flight
• Connect SIM7600 USB port (not USB-to-UART) to one available USB port on Raspberry.
• Connect 4G LTE Antenna to SIM7600 MAIN connector

Enable Rasperry Pi serial interface :

sudo raspi-config

• Go to Interfaces Options
• Then to Serial
• Hit No at question “Would you like a login shell to be accessible over serial?”
• Hit Yes at question “Would you like the serial port to be enabled?”
• Finish & restart Raspberry Pi

Install minicom to be able to send command to SIM7600 card later :

sudo apt-get update
sudo apt-get install minicom

Get file package from Waveshare with this code :

wget https://www.waveshare.com/w/upload/2/29/SIM7600X-4G-HAT-Demo.7z
sudo apt-get install p7zip-full
7z x SIM7600X-4G-HAT-Demo.7z   -r -o/home/pi
sudo chmod a+x /home/pi/SIM7600X-4G-HAT-Demo/Raspberry/c/sim7600_4G_hat_init

In your /etc/rc.local, you can add this line before “exit 0” :

/home/pi/SIM7600X-4G-HAT-Demo/Raspberry/c/sim7600_4G_hat_init

But when you will issue a reboot, you can not use your 4G card anymore.
For this, you need to add in a new file /etc/rc6.d/K00_sim7600_hat_stop :

echo "1" > /sys/class/gpio/gpio4/value
echo "1" > /sys/class/gpio/gpio6/value

Now, it’s time to chat with your SIM7600 card :

minicom -D /dev/ttyS0 # for Raspberry Pi 3
minicom -D /dev/ttyAMA0 # for Raspberry Pi 2B / Zero

You may need to provide APN & other settings to connect to Internet through your provider (next example is for Orange in France) :

AT+CGDCONT=1,"IPV4V6","orange","",0,0,0,0
AT+CGACT=1,1
AT+CUSBPIDSWITCH=9011,1,1

The last line switch modem in RNDIS mode, you will discover a new entry in ifconfig.

Commonly used commands (for more go to https://www.waveshare.com/w/upload/8/8f/SIM7500_SIM7600_Series_AT_Command_Manual_V1.12.pdf) :

ATI	Get informations about hardware
AT&F	Reset all parameters to defaults
AT+CFUN?	Returns 1 if full functionnality mode, 0 if minimal (check if gpio pins 4/6 are correctly set in rc.local)
AT+CPIN?	READY if connected, SIM PIN if PIN is needed
AT+CPIN=12345678	Push PIN code if needed to unlock SIM card
AT+CSPN?	Get SIM provider name
AT+CSQ	Query signal quality, first number must not be 99
AT+CRESET	Reset module