Specifications

LEON-G100/G200 - System Integration Manual
GSM.G1-HW-09002-C Preliminary System description
Page 44 of 75
1.11.1.2 UART signal behavior
See Table 2 for a description of operating modes and states referred to in this section.
By default the RxD and the TxD lines are set to the OFF state at UART initialization, following the boot sequence
when the module is switched on. The module holds RxD and TxD in the OFF state until data is either
transmitted or received by the module: an active pull-up is enabled inside the module on the TxD input.
The hardware flow control output (CTS line) indicates when the module is in active mode and the UART
interface is enabled: the module drives the CTS line to the ON state or to the OFF state when it is either prepared
or not prepared to accept data from the external device (DTE).
After the boot sequence the CTS line is set to the ON state at UART initialization, when the module is in active-
mode and ready to operate. By default the module automatically enters idle-mode (power saving) unless this
mode has been disabled using an AT command (see u-blox AT Commands Manual [2]).Thus data delivered by
the DTE can be lost if no hardware flow-control is enabled. The module periodically wakes up from idle-mode to
the active-mode to be synchronized with network activity. Idle-mode time is fixed by network parameters and
can be up to ~2.1 s. When the module wakes up to active-mode, the UART interface is enabled: the CTS line is
switched to the ON state and is held in this state for a minimum of ~11 ms.
The behavior of hardware flow-control output (CTS line) during the module normal operations (idle mode and
active mode) is illustrated in Figure 27.
The time delay for the module to go from active-mode to idle-mode is variable and depends (in addition to
dependency on network parameters) on the timeout from the last data received at the serial port. This timeout is
configurable by the AT+UPSV command, between 40 GSM frames (~184 ms) and 65000 GSM frames (~300 s)
Default value is 2000 GSM frames (~9.2 s).
Figure 27: CTS behavior during normal module operation: the CTS line indicates when the module is able (CTS = ON) or not able
(CTS = OFF) to accept data from the DTE and communicate through the UART interface
The hardware flow control input (RTS line) is set by default to OFF state at UART initialization at the end of the
boot sequence, after the module switch on. RTS line is then held by the module in the OFF state if hardware
flow- control is not enabled by the DTE: an active pull-up is enabled inside the module on the RTS input.
The module drives the DSR line to indicate whether it is ready to operate or not. After the module switches on,
the DSR line switches from ON state to OFF state as shown in Figure 28. During the Boot process of the module,
DSR is forced to OFF, until the module is not ready to operate. It is switched to ON state when the module is
ready to operate. The time T
switch
depends on the duration of the boot process, and is in the range of ~1 s.
Figure 28: DSR behavior at power-on
T
switch
0
DSR ON
DSR OFF
Power-on
0.024
time [s]
T
switch
0
DSR ON
DSR OFF
Power-on
0.024
time [s]
time [s]
CTS ON
CTS OFF
max ~2.1 s
UART disabled
min ~11 ms
UART enabled
~9.2 s (default)
UART enabled
Data input
time [s]
CTS ON
CTS OFF
max ~2.1 s
UART disabled
min ~11 ms
UART enabled
~9.2 s (default)
UART enabled