Problem communicating with WISMO 228 thru UART


I have problem getting any feedback from Wismo 228 connected through UART.
My layout is similar to one found on Rocketscream Tralog and uses all design examples and recommendations in Wismo’s technical application guide. I would like to emphasize that this is prototype board, so no GSM antenna is connected and power is supplied directly from laboratory DC power supply (GW INSTEK GPS-3303).
For UART communication a MAX3232 is used as level shifter. UART is connected through UART to serial cable and PC is communicating via Terminal application. MAX 3232 is powered by 2,9 V and is sending data to WISMO TXD pin. WISMO is operating in 2 - wire configuration (no flow control)

When I connect power supply to WISMO (3,6V Nom voltage) I receive WISMO READY signal (logical high), but when I send AT commands to WISMO, nothing is returned in reply… . I tried lowering RTS and DTR to logical low (gnd) but WISMO hasn’t stopped giving me “silence treatment” - RXD is not sending anything. All signal nominations (TXD, RXD, DTR, RTS) are same as in Wismo Technical Guide

Thank you in advance for your quick reply


What is meant by on sending AT commands nothing returned.Does it mean that no response is received for any AT command issued.Are you able to again issue any AT command once the response is not received or the module is completely hanged i.e. you are not able to issue any command further.


By default, the CTS & RTS control pin are enabled.
Try sorting them using a pair of tweezer, then disable them using the AT command.
It should work by then and you can release the tweezer (or anything you are comfortable with).
Always try with 115200 (I know it’s auto baud rate…) before anything else. It makes your life easier.

Glad someone is referencing my work!