Integrator's Manual GR47/GR48

5. SYSTEM CONNECTOR INTERFACE
49
LZT 123 7589 R1A
5.18 TX_ON - Burst Transmission
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
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
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.
Receive operation
Frequency I
2
C CLK
400 kHz
High or low I
2
C CLK
1.2 µs
Delay time after falling edge of I
2
C
CLK
100 ns
Hold time after falling edge of I
2
C
CLK
0ns
Parameter Min. Typ. Max. Units
Pin Signal Dir Description
35 TX_ON O GSM radio device to transmit
Pin Signal Dir Description
25 VRTC - Voltage for the Real Time Clock
Parameter Min. Typ. Max. Units
RTC accuracy 25°C 8 (21) 20 (52) ppm (s/month)
RTC accuracy extreme
temperatures
89 (231) 101 (262) ppm (s/month)