6 Replies Latest reply: Nov 12, 2015 7:39 AM by gabriel cuellar RSS

Telit GL865 dual serial port problem




I'm working on a project with Telit GL865 dual module. I have a problem connecting GL865 to PC (for sending AT commands).

Module itself turns on afer 3.8V applied on VBATT and VBATT_PA; PWRMON goes high.


I am using a FTDI MM232R board to interface between USB and GL865. To produce 2.8V I connected in series  3.3V pin, two diodes with ~0.2V drop and resistor. However, FTDI seems to function properly (watching TX signal on scope).


I have connected C104/RXD (GL865) to RXD (FTDI), C103/TXD (GL865) to TXD (FTDI), C105/RTS (Telit) to RTS# (FTDI), C106/CTS (Telit) to CTS# (FTDI) and GND to GND. DTR, DSR, RING and DCD pins are left unconnected. Aux serial port is also left unconnected. All GND pins and AGND pin are connected to ground. RESET pin is floating.


I'm using RealTerm to communicate - baud rate 57600, Hardware flow control is set to RTS/CTS. At the end of line terminal ads CR and LF "extension".


Afer applying 3.8V, GL865 goes on (PWRMON in high). I send a command AT, GL865 should answer OK, but it doesn't.

TXD from FTDI forms a signal (seems OK), RXD is high, CTS is low and RTS is high.

What am I doing wrong?

Could someone plesae help me with this PC - Telit GL865 dual connection.

If someone has already done a connection like this I would be grateful to have a circuit.


Thanks in advance!