GE865 Hardware User Guide
1vv0300799 Rev.9 – 27-07-2009
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved
page 42 of 70
9.3 5V UART level translation
If the OEM application uses a microcontroller with a serial port (UART) that works at a
voltage different from 2.8 - 3V, then a circuitry has to be provided to adapt the different
levels of the two set of signals. As for the RS232 translation there are a multitude of
single chip translators. For example a possible translator circuit for a 5V
TRANSMITTER/RECEIVER can be:
TIP:
Note that the TC7SZ07AE has open drain output; therefore the resistor R2 is
mandatory.
NOTE:
The UART input line TXD (rx_uart) of the GE865 is NOT internally pulled up with a
resistor, so there may be the need to place an external 47K
Ω
pull-up resistor, either the
DTR (dtr_uart) and RTS (rts_uart) input lines are not pulled up internally, so an external
pull-up resistor of 47K
Ω
may be required.