User's Manual

GE864
GE864GE864
GE864-
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-QUAD Automotive V2 Hardware User Guide
QUAD Automotive V2 Hardware User GuideQUAD Automotive V2 Hardware User Guide
QUAD Automotive V2 Hardware User Guide
1vv0300840 Rev.3 2010-04-08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 41 of 71
9.3.
9.3.9.3.
9.3. UART lev
UART levUART lev
UART level translation
el translationel translation
el 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:
TIP: TIP:
TIP:
The logic IC TC7SZ07AE may be used as level translator. Note that the TC7SZ07AE has
open drain output, therefore the resistor R2 is mandatory.
NOTE:
NOTE: NOTE:
NOTE:
The UART input line TXD (rx_uart) of the GE864-QUAD Automotive V2 is NOT internally
pulled up with a resistor, so there may be the need to place an external 47KΩ 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 47KΩ may be required.
A power source of the internal interface voltage corresponding to the 2.8VCMOS high
level is available at the PWRMON pin on the connector, whose absolute maximum
output current is 1mA.
A maximum of 9 resistors of 47 KΩ pull-up can be connected to the PWRMON pin,
provided no other devices are connected to it and the pulled-up lines are GE864-QUAD