SIM225 Technical Reference Manual
43
© Serious Integrated, Inc.
SIM225_TRM_A1ENUS
Revision A1
RTCC BATTERY BACKUP
The RX63x MCU has several power inputs, including a “main” 3.3V power input connected to the main
module power along with a backup battery power input pin. The RTCC is normally powered from the main
module power. When main power fails it automatically switches to battery power (if available).
Some family members of the SIM225 have on-module
clock/calendar battery holder
designed to
accommodate an industry standard CR2032 coin cell battery. This coin cell battery is connected to the
RTCC battery backup voltage input on the RX63x MCU.
With a good quality battery, the clock/calendar could run for up to several years without replacement.
Consult the
RX MCU
data sheet or
Contact Renesas
for detailed assistance in calculating battery life
expectations in your specific end-usage model.
RTCC REAL TIME CLOCK TEMPERATURE COMPENSATION
Like all timekeeping devices, the RTCC will drift over time. Few timepieces are perfectly accurate! The drift
and resulting inaccuracy are determined by the accuracy of the 32.768 KHz oscillator. Temperature
variance is the most common culprit: crystals have slight variations in frequency over temperature.
The RX63x MCU Family RTC peripheral has a Time Error Adjustment Register (RADJ) which, when
combined with the SIM225’s on-MCU and/or on-PCB temperature sensor, could be used with custom
software to improve the accuracy over temperature of the RTCC.
Contact Renesas
for assistance if your
application requires this level of precision in your specific end-usage model.
USER PUSHBUTTON SWITCH AND LEDS
Some SIM225 variants have a single end-user-friendly pushbutton switch on the display-side of the
module near the LCD panel. The switch is connected to an MCU input that is both a general purpose input
and also an interrupt input that can wake the MCU from various sleep modes. A front panel captive
button or plunger can be positioned to actuate this switch. There is no requirement for an end-system to
use this switch; the enclosure may cover it completely and render it inaccessible if desired.
Some SIM225 variants have two bi-color red-green LEDs placed on front of the display-side of the
module. A bi-color LED is actually two independent LEDs in one package: the LED on the SIM225 has red
and green LEDs that, when both are on, have an amber hue. Typically, a plastic or metal front panel
enclosure will expose this LED through a plastic light pipe; for example, the
BiVar PLP1-125-F
. There is no
requirement for an end-system to expose this LED. The enclosure may cover it completely and render it
un-viewable if desired.
Signal
Description
MCU Port
SW1#
Switch Input (active low)
P07
LEDRR
LED Right Red
P90/LED0
LEDRG
LED Right Green
P91/LED1
LEDLR
LED Left Red
P92/LED2
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