RELEASE
Revision B1
©Serious Integrated, Inc.
30
The
PJ8/PWM2A-BLEN
signal drives the enable input of an On Semi CAT4139 or equivalent LED booster chip. The boost
controller delivers a constant 45-160mA (dependent on the LCD option) to the LCD’s LED array via signals
and
BL_LED-
.
Backlight power is a significant portion of the SIM’s power consumption. Software should carefully manage the
backlight to be powered on as infrequently and for as short a time as possible – especially in battery powered systems,
but also to ensure backlight longevity. Reducing the backlight power can significantly extend backlight lifetimes.
Typically, operating the backlight at 50% brightness can more than double the backlight lifetime.
Software algorithms can enable the PWM capability of the
PJ8/PWM2A-BLEN
pin to enable backlight dimming. A PWM
driven by a typical 1 KHz clock with 16 PWM steps for a PWM net frequency of 64 Hz is generally sufficient and flicker
free with duty cycles from 0 to 100%. In no circumstances should the PWM clock exceed 16 KHz.
The
proximity
and
ambient light
sensing features (where available) can be used to assist in extending backlight
longevity by dynamically adjusting the backlight power through software.
The display backlight is a significant power load on the system. When turned on there is an inherent short term
power surge as well an overall power demand increase. If
+VEXT
is too low, the impedance of the external power
supply too high, and/or the transient current support of the supply insufficient, then the SIM can reset. Observe the
minimum recommended
+VEXT
DC Maximum Ratings
carefully.
The
Serious Human Interface™ Platform
has the backlight driver included; setting the platform glass backlight value
to 0 to 100% automatically modulates the dimming circuit.
BATTTERY BACKED REAL TIME CLOCK/CALENDAR (RTCC):
+VBAT
Some SIM535 variants have an
External RTCC with Optional Battery Backup
chip with the battery holder option for a
common CR1025-type 3V coin cell battery populated. This is not designed to be a rechargeable battery, nor does any
circuit on the SIM535 supply power to charge this battery. The only purpose and connection of this coin cell battery is to
provide the backup power signal
+VBAT
to the RTCC chip to keep the clock/calendar running in the event that all other
power sources are removed. This battery can keep the clock keeping time for up to several years without replacement.
The RTCC automatically switches to use the coin cell power only when main power is not available, so in a system that
normally has main power applied the coin cell battery is rarely used. See
External RTCC
for more information.
MEMORY
SERIAL FLASH
All SIM535 family members include the SST
SST25VF064C
serial FLASH, a 64 megabit (8 megabyte) device with 2048
4KByte erasable blocks as well as a built-in 64-bit unique serial ID and 192 bits of
OTP ID space.
The serial FLASH device is connected to SPI Channel 0 of the MCU:
Schematic
Signal Name
Description
FLASH
Name
MCU
Name
PB19-MOSI0
SPI data MCU
FLASH
SDI
PB19/MOSI0
PB20-MISO0
SPI data FLASH
MCU
SDO
PB20/MISO0
PB17-RSPCK0
SPI FLASH clock
SCK
PB17/RSPCK0
PB18-SSL00
FLASH slave select
CS#
PB18/SSL00#
PF2-SFRST#
Serial FLASH RESET#
HOLD#/RES#
PF2
See the
SST25VF064C data sheet
for hardware specifications and programming details and the Renesas SH7269
datasheet for information on the SPI master port configuration.
PF2
is a generic I/O pin on the SH7269 and is wired
(with a weak pull-up) to the FLASH’s
RESET#
input. Left unprogrammed, the FLASH will self-reset on power-up and be in
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