MCF51EM256CLL Freescale Semiconductor, MCF51EM256CLL Datasheet - Page 421

• Manufacturer Part Number: MCF51EM256CLL
• Description: IC MCU 32BIT 256KB FLASH 100LQFP
• Manufacturer: Freescale Semiconductor
• Series: MCF51EMr

Specifications of MCF51EM256CLL

• Core Processor: Coldfire V1
• Core Size: 32-Bit
• Speed: 50MHz
• Connectivity: I²C, SCI, SPI
• Peripherals: LCD, LVD, PWM, WDT
• Number Of I /o: 63
• Program Memory Size: 256KB (256K x 8)
• Program Memory Type: FLASH
• Ram Size: 16K x 8
• Voltage - Supply (vcc/vdd): 1.8 V ~ 3.6 V
• Data Converters: A/D 16x12b
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 100-LQFP
• Processor Series: MCF51EM
• Core: ColdFire V1
• Data Bus Width: 32 bit
• Data Ram Size: 16 KB
• Interface Type: RS-232, LIN
• Maximum Clock Frequency: 50 MHz
• Number Of Timers: 3
• Operating Supply Voltage: 1.8 V to 3.6 V
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• 3rd Party Development Tools: JLINK-CF-BDM26, EWCF
• Development Tools By Supplier: DEMOEM
• Minimum Operating Temperature: - 40 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Eeprom Size: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

17.7.4
17.7.5
17.8
17.8.1
The compensation circuit provides an accurate and wide compensation range, which is suitable for many
crystals, and can correct errors as high as 3906 PPM and as low as 0.119 PPM. The same hardware logic
supports both temperature compensation and frequency compensation.
To perform temperature compensation the CPU maintains a look-up-table which lists the change in
frequency of crystal for each degree change in temperature. CPU wakes up periodically to measure the
external temperature via a temperature sensor connected to an A/D converter. CPU uses the look-up-table
to determine the compensation factor and writes the value to be compensated (in terms of number of IRTC
oscillator clock cycles in 2’s complement format) in the IRTC compensation register (IRTC_COMPEN).
Based on the value written the hardware add/remove pulses accordingly to adjust the 1 Hz frequency due
to variation on temperature.
To perform crystal compensation, the calculation of correction is done by firmware using crystal
characteristics, where the CPU sets the correction factor in the two’s complement format in the same IRTC
compensation register (IRTC_COMPEN). Based on the values written in the IRTC_COMPEN register, the
circuit compensates by adding/skipping pulses in the oscillator clock signal.
There are two important components in the compensation algorithm viz. Compensation value and
compensation interval. These are defined as:
Freescale Semiconductor
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CPU should enable the tamper detect pins when the configuration of IRTC is complete. If not, it is
automatically enabled 15 seconds after power on.
IRTC has one tamper detect pin. High level input on this pin is considered as a tamper and an
interrupt is generated if the tamper interrupt is enabled.
Whenever the battery power is removed and MCU power is ON, it is considered as a tamper and a
time stamp of that event is stored. In case the battery is removed as a part of maintenance then the
application should take care of this and not indicate a tamper.
An interrupt is sent to CPU. The IRTC interrupt service routine should read the Interrupt Status
Register to determine if a tamper had occurred.
CPU performs calculations (external to IRTC) to determines the correction factor in the 1 Hz clock
to remove any variations that might creep into the 32 kHz Oscillator Clock due to Temperature or
Crystal. Calibration procedure done in software provides the correction factor which is used by
compensation hardware.
Application programs this correction factor into the IRTC registers, hardware within the IRTC
compensates the clock to output balanced compensation interval.
IRTC is said to be calibrated but this performed is done every user-defined interval
Block Description (Brief Overview)
IRTC Tamper Detect
IRTC Calibration
Compensation Logic
MCF51EM256 Series ColdFire Integrated Microcontroller Reference Manual, Rev. 8
Independent Robust Real Time Clock (IRTC)
17-37