LPC2921 datasheet(39/83 Pages) NXP

39 / 83 page

LPC2921_23_25_1

Preliminary data sheet

Rev. 01 — 15 June 2009

39 of 83

NXP Semiconductors

LPC2921/2923/2925

ARM9 microcontroller with CAN, LIN, and USB

6.14.6.1

Pin description

MSCSS timer 0 has no external pins.

MSCSS timer 1 has a PAUSE pin available as external pin. The PAUSE pin is combined

with other functions on the port pins of the LPC2921/2923/2925. Table 22 shows the

MSCSS timer 1 external pin.

6.14.6.2

Clock description

The Timer modules in the MSCSS are clocked by CLK_MSCSS_MTMRx (x = 0 to 1), see

Section 6.7.2. Note that each timer has its own CLK_MSCSS_MTMRx branch clock for

power management. The frequency of all these clocks is identical to CLK_MSCSS_APB

since they are derived from the same base clock BASE_MSCSS_CLK.

Note that, unlike the timer modules in the Peripheral SubSystem, the actual timer counter

registers run at the same clock as the APB system interface CLK_MSCSS_APB. This

clock is independent of the AHB system clock.

If a timer module is not used its CLK_MSCSS_MTMRx branch clock can be switched off.

6.14.7 Quadrature Encoder Interface (QEI)

A quadrature encoder, also known as a 2-channel incremental encoder, converts angular

displacement into two pulse signals. By monitoring both the number of pulses and the

relative phase of the two signals, the user can track the position, direction of rotation, and

velocity. In addition, a third channel, or index signal, can be used to reset the position

counter. The quadrature encoder interface decodes the digital pulses from a quadrature

encoder wheel to integrate position over time and determine direction of rotation. In

addition, the QEI can capture the velocity of the encoder wheel.

The QEI has the following features:

• Tracks encoder position.

• Increments/ decrements depending on direction.

• Programmable for 2x or 4x position counting.

• Velocity capture using built-in timer.

• Velocity compare function with less than interrupt.

• Uses 32-bit registers for position and velocity.

• Three position compare registers with interrupts.

• Index counter for revolution counting.

• Index compare register with interrupts.

• Can combine index and position interrupts to produce an interrupt for whole and

partial revolution displacement.

• Digital ﬁlter with programmable delays for encoder input signals.

• Can accept decoded signal inputs (clk and direction).

• Connected to APB.

Table 22.

MSCSS timer 1 pin

Symbol

Direction

Description

MSCSS PAUSE

pause pin for MSCSS timer 1

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