In our design the microcontroller is powered by 3.3V.
The GE865 hardware specification says that the
input high logic level voltage should be 2.8V (3.1V max).
What is the best way to connect the microcontroller output lines
(TX, DTR, RTS) to the GE865 to comply with the specification ?
(the serial port baud-rate is 115200bps)
– Resistor voltage divider ?
– Transistor circuit ?
Connect them directly. Do not worry about level difference, but take in mind to activate microcontroller’s UART after powering GE865 to prevent latch-up problems.
I am using PIC24FJ64GA102 (3,3V power supply) connected to SER2 (ASC1).
The manual explicitly informs the maximum input
voltage level for the pins as 3.1V.
Are you sure this will not danify the modem ?
A technical support person from Telit in Brazil
suggested using a resistor voltage divider.
This is a very common problem so I think
Telit should post a note in the user manual
with a recomendation for this situation.
In all designs in my company, using GE863, GE864, GE865 and GL865, 3.3V outputs from MCU or other IC are directly connected to modules inputs. No damages.
But if you prefere – put a resistive voltage dividers
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