LISA-C2 series and FW75-C200 - System Integration Manual
UBX-13000620 - R21
Early Production Information
System description
Page 45 of 103
PCM_CLK
frequency is fixed 128 KHz
PCM_DOUT
,
PCM_DIN
data are 16 bit words with 8 kHz sampling rate, mono. Data is in 2’s complement
notation. MSB is transmitted first
When
PCM_SYNC
toggles high, the first synchronization bit is always low. Second synchronization bit (present
only in case of 2 bit long
PCM_SYNC
configuration) is MSB of the transmitted word (MSB is transmitted twice in
this case)
PCM_DOUT
changes on
PCM_CLK
rising edge,
PCM_DIN
changes on
PCM_CLK
falling edge
Additional considerations
Any external signal connected to the PCM interfaces must be tri-stated when the module is in power-down
mode, when the external reset is forced low and during the module power-on sequence (at least for 3 s
after the start-up event), to avoid latch-up of circuits and allow a proper boot of the module. If the external
signals connected to the wireless module cannot be tri-stated, insert a multi channel digital switch (e.g.
Texas Instruments SN74CB3Q16244, TS5A3159, or TS5A63157) between the two-circuit connections and
set to high impedance during module power down mode, when external reset is forced low and during
power-on sequence.
LISA-C200: Pay special attention when using voltage level shifter connections. V_INT (1.8 V) is
provided to support biasing of level shifter ASICs. A problem can result with certain level shifter
interface buffers, which can back feed voltage to the V_INT line preventing the modem from
powering off and/or resetting properly. The back feed voltage typically comes from a host output
through the level shifter and out either from the level shifter VCC pin connected to V_INT or to
the modem PCM input lines though an internal protection diode with modem. With modem
VCC = 0 V, a measured voltage can range from 0.3 to 1.0 V on the V_INT, preventing modem from
ever resetting or powering up or down properly.
1.12
General Purpose Input / Output (GPIO)
Network status through GPIO, is supported only by LISA-C200 from version 04S / 24S onwards.
LISA-C series modules provide 5 pins (
GPIO1
-
GPIO5
) which can be configured as general purpose input or
output, or can be configured to provide special functions via u-blox AT commands. (For further details, refer to
u-blox C2 series AT Commands Manual
[3], +UGPIOC, +UGPIOR, +UGPIOW, +UGPS, +UGPRF).
The following functions are available in the LISA-C modules:
•
Network status indication:
The
GPIO1
,
GPIO2
,
GPIO3
,
GPIO4
or
GPIO5
can be configured to indicate network status (i.e. no service,
registered home network, registered visitor network, voice or data call session), by means of the
AT+UGPIOC command.
No GPIO pin is by default configured to provide the “Network status indication” function.
The “Network status indication” mode can be configured to only one pin at a time; it is not possible to
simultaneously set the same mode on another pin.
See section 3.9, for further details.
