SC312XDP512F0MPVR datasheet(359/1348 Pages) FREESCALE

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Chapter 7 Enhanced Capture Timer (S12ECT16B8CV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

359

7.4.1.2

OC Channel Initialization

Internal register whose output drives OCx when TIOS is set, can be force loaded with a desired data by

writing to CFORC register before OCx is conﬁgured for output compare action. This allows a glitch free

switch over of port from general purpose I/O to timer output once the output compare is enabled.

7.4.1.3

Pulse Accumulators

There are four 8-bit pulse accumulators with four 8-bit holding registers associated with the four IC

buffered channels 3–0. A pulse accumulator counts the number of active edges at the input of its channel.

The minimum pulse width for the PAI input is greater than two bus clocks.The maximum input frequency

on the pulse accumulator channel is one half the bus frequency or Eclk.

The user can prevent the 8-bit pulse accumulators from counting further than 0x00FF by utilizing the

PACMX control bit in the ICSYS register. In this case, a value of 0x00FF means that 255 counts or more

have occurred.

Each pair of pulse accumulators can be used as a 16-bit pulse accumulator (see Figure 7-70).

Pulse accumulator B operates only as an event counter, it does not feature gated time accumulation

mode.The edge control for pulse accumulator B as a 16-bit pulse accumulator is deﬁned by TCTL4[1:0].

To operate the 16-bit pulse accumulators A and B (PACA and PACB) independently of input capture or

output compare 7 and 0 respectively, the user must set the corresponding bits: IOSx = 1, OMx = 0, and

OLx = 0. OC7M7 or OC7M0 in the OC7M register must also be cleared.

There are two modes of operation for the pulse accumulators:

•

Pulse accumulator latch mode

The value of the pulse accumulator is transferred to its holding register when the modulus

down-counter reaches zero, a write 0x0000 to the modulus counter or when the force latch control

bit ICLAT is written.

At the same time the pulse accumulator is cleared.

•

Pulse accumulator queue mode

When queue mode is enabled, reads of an input capture holding register will transfer the contents

of the associated pulse accumulator to its holding register.

At the same time the pulse accumulator is cleared.

7.4.1.4

Modulus Down-Counter

The modulus down-counter can be used as a time base to generate a periodic interrupt. It can also be used

to latch the values of the IC registers and the pulse accumulators to their holding registers.

The action of latching can be programmed to be periodic or only once.

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