SYSTEM CONNECTOR INTERFACE
50
LZT 123 8020 R1A
Hold time after falling edge of I
2
C CLK
0
ns
5.18 TX_ON - Burst Transmission
Pin Signal Dir Description
35
TX_ON
O
GSM radio device to transmit
Burst transmission is the time when a GSM transceiver unit is
transmitting RF signals. TX_ON indicates the radio device is
going into transmission mode.
5.19 Real Time Clock
Pin Signal
Dir
Description
25
VRTC
-
Voltage for the Real Time Clock
The Real Time Clock (RTC) provides the main microprocessor
with a time-of-day calendar and alarm, and a one-hundred-year
calendar. Its accuracy is shown in the table below
Parameter Min.
Typ. Max. Units
RTC accuracy
25ûC
8 (21)
20 (52)
ppm (s/month)
RTC accuracy
extreme
temperatures
89 (231)
101
(262)
ppm (s/month)
The Real Time Clock operates in two modes when connected
to a separate power supply:
•
RTC normal mode: the radio device is in ON or OFF mode
and it is supplied with power (VCC is applied).
•
RTC back-up mode: VCC is disconnected and the RTC is
maintained by a separate backup power supply connected
to the VRTC input (see Figure 5.13 below).
Backup power is provided by a capacitor, golden-capacitor or
battery in your application and must be connected to the VRTC
pin. During RTC normal operation, the back up source will be
charged.
In back-up mode, the back-up source must provide enough
power for RTC operation. Refer to the table for the amount of
current required.
The following table shows voltage characteristics for both
modes.
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