Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 83 of 175
If the SPI/IPC interface is not used, the SPI_MOSI, SPI_MISO, SPI_SCLK, SPI_MRDY, SPI_SRDY pins can
be left unconnected.
Any external signal connected to the SPI / IPC interface 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 cellular 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.
1.9.5 MUX Protocol (3GPP 27.010)
LISA-U2 modules have a software layer with MUX functionality, 3GPP TS 27.010 Multiplexer Protocol [6],
available either on the UART or on the SPI physical link. The USB interface does not support the multiplexer
protocol.
This is a data link protocol (layer 2 of OSI model) which uses HDLC-like framing and operates between the
module (DCE) and the application processor (DTE) and allows a number of simultaneous sessions over the used
physical link (UART or SPI): the user can concurrently use AT command interface on one MUX channel and
Packet-Switched / Circuit-Switched Data communication on another MUX channel. The multiplexer protocol can
be used on one serial interface (UART or SPI) at a time. Each session consists of a stream of bytes transferring
various kinds of data such as SMS, CBS, PSD, GNSS, AT commands in general. This permits, for example, SMS to
be transferred to the DTE when a data connection is in progress.
The following virtual channels are defined:
 Channel 0: control channel
 Channel 1 – 5: AT commands / data connection
 Channel 6: GNSS tunneling
 Channel 7: SAP (SIM Access Profile)
For more details see the Mux implementation Application Note [15].
If the module switch off AT command +CPWROFF is issued over a multiplexer channel, the completion of
the module power off sequence could require up to 2.5 s, after the module OK reply. Therefore, if the
Application Processor (AP) controls the VCC supply of the module, the AP should disable the multiplexer
protocol and then issue the AT+CPWROFF command over the used AT interface, or otherwise the AP
should issue the AT+CPWROFF command over a multiplexer channel and wait 2.5 s after OK reception
before removing the module VCC supply.