LPC1837FET256,551 NXP Semiconductors, LPC1837FET256,551 Datasheet - Page 710

• Manufacturer Part Number: LPC1837FET256,551
• Description: Microcontrollers (MCU) 32BIT ARM CORTEX-M3 MCU 136KB SRAM
• Manufacturer: NXP Semiconductors
• Series: LPC18xxr

Specifications of LPC1837FET256,551

• Core: ARM Cortex M3
• Core Processor: ARM® Cortex-M3™
• Core Size: 32-Bit
• Speed: 150MHz
• Connectivity: CAN, EBI/EMI, Ethernet, I²C, Microwire, SD/MMC, SPI, SSI, SSP, UART/USART, USB OTG
• Peripherals: Brown-out Detect/Reset, DMA, I²S, Motor Control PWM, POR, PWM, WDT
• Number Of I /o: 80
• Program Memory Size: 1MB (1M x 8)
• Program Memory Type: FLASH
• Eeprom Size: -
• Ram Size: 136K x 8
• Voltage - Supply (vcc/vdd): 2 V ~ 3.6 V
• Data Converters: A/D 16x10b; D/A 1x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 256-LBGA
• Lead Free Status / Rohs Status: Details
• Other names: 935293795551

NXP Semiconductors
31.7 Functional description
<Document ID>
User manual
31.7.1 Calibration procedure
Table 660. Alarm Year register (AYRS - address 0x4004 607C) bit description
[1]
The calibration logic can periodically adjust the time counter either by not incrementing
the counter, or by incrementing the counter by 2 instead of 1. This allows calibrating the
RTC oscillator under some typical voltage and temperature conditions without the need to
externally trim the RTC oscillator.
A recommended method for determining the calibration value is to use the CLKOUT
feature to unintrusively observe the RTC oscillator frequency under the conditions it is to
be trimmed for, and calculating the number of clocks that will be seen before the time is off
by one second. That value is used to determine CALVAL.
The exact method of calibration depends on whether CALVAL is even or odd. For even
values, the hardware performs a two calibrations sequentially multiple times (one
calibration at CALVAL+1 and one calibration at CALVAL - 1) and averages both calibration
values. For odd values of CALVAL, the calibration time is accurate.
If the RTC oscillator is trimmed externally, the same method of unintrusively observing the
RTC oscillator frequency may be helpful in that process.
Backward calibration
Enable the RTC timer and calibration in the CCR register (set bits CLKEN = 1 and
CCALEN = 0). In the CALIBRATION register, set the calibration value CALVAL  1 and
select CALDIR = 1.
Forward calibration
Enable the RTC timer and calibration in the CCR register (set bits CLKEN = 1 and
CCALEN = 0). In the CALIBRATION register, set the calibration value CALVAL  1 and
select CALDIR = 0.
Bit
11:0
31:4
•
•
•
•
•
This register value is not changed by reset.
The SEC timer and the calibration counter count up for every 1 Hz clock cycle.
When the calibration counter reaches CALVAL, a calibration match occurs and all
RTC timers will be stopped for one clock cycle so that the timers will not increment in
the next cycle.
If an alarm match event occurs in the same cycle as the calibration match, the alarm
interrupt will be delayed by one cycle to avoid a double alarm interrupt.
The SEC timer and the calibration counter count up for every 1 Hz clock cycle.
When the calibration counter reaches CALVAL, a calibration match occurs and the
RTC timers are incremented by 2.
Symbol
YEAR
-
All information provided in this document is subject to legal disclaimers.
Rev. 00.13 — 20 July 2011
Description
Year value in the range of 0 to 4095.
Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined.
Chapter 31: LPC18xx Real-Time Clock (RTC)
UM10430
© NXP B.V. 2011. All rights reserved.
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Reset
value
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[1]