AC75 Hardware Interface Description
Strictly confidential / Preliminary
s
AC75_HD_V00.202
Page 27 of 120
27.04.2006
Assertion of CTS indicates that the module is ready to receive data from the host application.
In addition, if configured to a fixed bit rate (AT+IPR
≠
0), the module will send the URC
“^SYSSTART” or “^SYSSTART AIRPLANE MODE” which notifies the host application that
the first AT command can be sent to the module. The duration until this URC is output varies
with the SIM card and may take a couple of seconds.
Please note that no “^SYSSTART” or “^SYSSTART AIRPLANE MODE” URC will be
generated if autobauding (AT+IPR=0) is enabled.
To allow the application to detect the ready state of the module we recommend using
hardware flow control which can be set with AT\Q or AT+ICF (see [1] for details). The default
setting of AC75 is AT\Q0 (no flow control) which shall be altered to AT\Q3 (RTS/CTS
handshake). If the application design does not integrate RTS/CTS lines the host application
shall wait at least for the “^SYSSTART” or “^SYSSTART AIRPLANE MODE” URC. However,
if the URCs are neither used (due to autobauding) then the only way of checking the
module’s ready state is polling. To do so, try to send characters (e.g. “at”) until the module is
responding.
See also Chapter 3.3.2 “Signal States after Startup”
EMERG_RST
VEXT
TXD0/TXD1/RTS0/RST1/DTR0 (driven by the application)
CTS0/CTS1/DSR0/DCD0
ca. 500 ms
Interface pins
Undefined
Defined
PWR_IND
t = 400ms
min
>
120ms
BATT+
IGT
HiZ
Figure 5: Power-on with operating voltage at BATT+ applied before activating IGT
