User's Manual

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Note d’étude / Technical document : URD1– OTL

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4.15 UART SIGNALS AT POWER ON

The UART signals are low level active therefore these signals rise up when the module starts. During around

70ms (see figure below), those signals present a transient spike. Those spikes behaviour at start up are normal,

however pay attention to them when a CTS low level detection is used do send AT commands. Only DSR and

CTS signals get low after the end of the start up procedure.

Figure 36: Full UART signals during the power on sequence.

Module is ready to

receive AT commands

TXD

RXD

DTR

DCD

DSR

RTS

Module UART

interface is ON

Typ 5 seconds

Max 7 seconds

70ms

30ms

150ms

Transients spikes

during power on

sequence

Module is

OFF

Module is ON

POK_IN

2000ms

CTS