SAM4S16C Atmel Corporation, SAM4S16C Datasheet - Page 291

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SAM4S16C

Manufacturer Part Number
SAM4S16C
Description
Manufacturer
Atmel Corporation
Datasheets

Specifications of SAM4S16C

Flash (kbytes)
1024 Kbytes
Pin Count
100
# Of Touch Channels
32
Hardware Qtouch Acquisition
No
Max I/o Pins
79
Ext Interrupts
79
Usb Transceiver
1
Quadrature Decoder Channels
2
Usb Speed
Full Speed
Usb Interface
Device
Spi
3
Twi (i2c)
2
Uart
4
Ssc
1
Sd / Emmc
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
16
Adc Resolution (bits)
12
Adc Speed (ksps)
1000
Analog Comparators
1
Resistive Touch Screen
No
Dac Channels
2
Dac Resolution (bits)
12
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
128
Self Program Memory
YES
External Bus Interface
1
Dram Memory
No
Nand Interface
Yes
Picopower
No
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8/3.3
Operating Voltage (vcc)
1.62 to 3.6
Fpu
No
Mpu / Mmu
Yes / No
Timers
6
Output Compare Channels
6
Input Capture Channels
6
Pwm Channels
4
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
15.5.6
11100A–ATARM–28-Oct-11
11100A–ATARM–28-Oct-11
RTC Accurate Clock Calibration
The crystal oscillator that drives the RTC may not be as accurate as expected mainly due to
temperature variation. The RTC is equipped with circuitry able to correct slow clock crystal drift.
To compensate for possible temperature variations over time, this accurate clock calibration cir-
cuitry can be programmed on-the-fly and also programmed during application manufacturing, in
order to correct the crystal frequency accuracy at room temperature (20-25°C). The typical clock
drift range at room temperature is ±20 ppm.
In a temperature range of -40°C to +85°C, the 32.768 KHz crystal oscillator clock inaccuracy can
be up to -200 ppm.
The RTC clock calibration circuitry allows positive or negative correction in a range of 1.5 ppm to
1950 ppm. The calibration step error remains:
The calibration circuitry acts by slightly modifying the 1 Hz clock period from time to time. When
the period is modified, depending on the sign of the correction, the 1 Hz clock period increases
or reduces by around 4 ms. The period interval between 2 correction events is programmable in
order to cover the possible crystal oscillator clock variations.
The inaccuracy of a crystal oscillator at typical room temperature (±20 ppm at 20-25 degrees
Celsius) can be compensated if a reference clock/signal is used to measure such inaccuracy.
This kind of calibration operation can be set up during the final product manufacturing by means
of measurement equipment embedding such a reference clock. The correcting value must be
programmed into the RTC Mode Register (RTC_MR) and this value will be kept as long as the
circuitry is powered (backup area). Removing the backup power supply cancels this calibration.
This room temperature calibration can be further processed by means of the networking capabil-
ity of the target application.
To ease the comparison of the inherent crystal accuracy with the reference clock/signal during
manufacturing, an internal prescaled 32.768KHz clock derivative signal can be assigned to drive
RTCOUT0, RTCOUT1 outputs. To accommodate the measure, several clock frequencies can
be selected among 1 Hz, 32 Hz, 64 Hz, 512 Hz.
In any event, this adjustment does not take into account the temperature variation.
The frequency drift (up to -200 ppm) due to temperature variation can be compensated using a
reference time if the application can access such a reference. If a reference time cannot be
used, a temperature sensor can be placed close to the crystal oscillator in order to get the oper-
ating temperature of the crystal oscillator. Once obtained, the temperature may be converted
using a lookup table (describing the accuracy/temperature curve of the crystal oscillator used)
and RTC_MR configured accordingly. The calibration can be performed on-the-fly. This adjust-
ment method is not based on a measurement of the crystal frequency/drift and therefore can be
improved by means of the networking capability of the target application.
If no crystal frequency adjustment has been done during manufacturing, it is still possible to do.
In the case where a reference time of day can be obtained through LAN/WAN network, it is pos-
sible to calculate the drift of the application crystal oscillator by comparing the values read on
RTC Time Register (RTC_TIMR) and programming the HIGHPPM and CORRECTION bitfields
below 1 ppm in a range from1.5 up to 90 ppm,
below 2 ppm from 90 ppm up to 130 ppm,
below 5 ppm from 130 ppm up to 200 ppm.
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