“It is correct that you only need RxD and TxD for module configuration and normal use. CONFIG, RTS and CTS are optional.
To set the module in test mode you need to enter configuration mode by sending 0x00 to RxD and wait for ‘>’ (0x3E) on TxD . Then enter Test mode 1 you send ‘1’ (0x31) to RxD and wait for ‘>’ (0x3E) on TxD again. Optionally you may enter config by assert CONFIG pin low instead of sending 0x00 on RxD.
For firmware upgrade you need Pin 19, pin 20, Reset, GND and VCC as described in the datasheet page 16.
Last Update: November 9, 2017