LPC1837FET256,551 NXP Semiconductors, LPC1837FET256,551 Datasheet - Page 683

• 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
<Document ID>
User manual
27.7.4 Velocity compare
cleared. The velocity timer is loaded with the contents of the velocity reload register
(LOAD). Finally, the velocity interrupt (TIM_Int) is asserted. The number of edges counted
in a given time period is directly proportional to the velocity of the encoder.
Setting the reset velocity bit (RESV) will clear the velocity counter, reset the velocity
capture register to 0xFFFF FFFF, and load the velocity timer with the contents of the
velocity reload register (LOAD).
The following equation converts the velocity counter value into an RPM value:
RPM = (PCLK  Speed  60) / Load  PPR  Edges)
where:
For example, consider a motor running at 600 rpm. A 2048 pulse per revolution
quadrature encoder is attached to the motor, producing 8192 phase edges per revolution.
With clocking on both PhA and PhB edges, this results in 81,920 pulses per second (the
motor turns 10 times per second). If the timer were clocked at 10,000 Hz, and the load
value was 2,500 (¼ of a second), it would count 20,480 pulses per update. Using the
above equation:
RPM = (10000  20480  60) / (2500  2048  4) = 600 RPM
Now, consider that the motor is sped up to 3000 RPM. This results in 409,600 pulses per
second, or 102,400 every ¼ of a second. Again, the above equation gives:
RPM = (10000  102400  60) / (2500  2048  4) = 3000 RPM
In addition to velocity capture, the velocity measurement system includes a
programmable velocity compare register. After every velocity capture event the contents
of the velocity capture register (CAP) is compared with the contents of the velocity
compare register (VELCOMP). If the captured velocity is less than the compare value an
interrupt is asserted provided that the velocity compare interrupt enable bit is set. This can
be used to determine if a motor shaft is either stalled or moving too slow.
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•
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PCLK is the QEI controller clock.
PPR is the number of pulses per revolution of the physical encoder.
Edges is 2 or 4, based on the capture mode set in the CON register (2 for CapMode
set to 0 and 4 for CapMode set to 1)
All information provided in this document is subject to legal disclaimers.
Rev. 00.13 — 20 July 2011
Chapter 27: LPC18xx Quadrature Encoder Interface (QEI)
UM10430
© NXP B.V. 2011. All rights reserved.
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