Rainbow Electronics GE863-PY - Manual (Page 45)

GE863 Hardware User Guide
1vv0300783 Rev.0 - 10/06/08
Reproduction forbidden without Telit Communications S.p.A. written authorization - All Rights Reserved page 45 of 80
NOTE: The UART input line TXD (rx_uart) of the GE863 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 VAUX pin.
A maximum of 9 resistors of 47 KΩ pull-up can be connected to the VAUX pin, provided no other
devices are connected to it and the pulled-up lines are GE863 input lines connected to open collector
outputs in order to avoid latch-up problems on the GE863.
Care must be taken to avoid latch-up on the GE863 and the use of this output line to power electronic
devices shall be avoided, especially for devices that generate spikes and noise such as switching level
translators, micro controllers, failure in any of these condition can severely compromise the GE863
functionality.
NOTE: The input lines working at 2.8VCMOS can be pulled-up with 47KΩ resistors that can be connected directly to
the VAUX line provided they are connected as in this example.
It is important to consider that the added circuit must have consumption lower than 1mA.
In case of reprogramming of the module has to be considered the use of the RESET line to start correctly the
activity.
The preferable configuration is having an external supply for the buffer.