ST10 datasheet(17/65 Pages) STMICROELECTRONICS

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ST10C167

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VIII - CAPTURE/COMPARE (CAPCOM) UNIT

The ST10C167 has two 16 channel CAPCOM

units. They support generation and control of

timing sequences on up to 32 channels with a

maximum resolution of 320ns at 25MHz CPU

clock. The CAPCOM units are typically used to

handle high speed I/O tasks such as pulse and

waveform generation, pulse width modulation

(PMW), Digital to Analog

(D/A) conversion,

software timing, or time recording relative to

external events.

Four 16-bit timers (T0/T1, T7/T8) with reload

registers provide two independent time bases for

the capture/compare register array.

The input clock for the timers is programmable to

several prescaled values of the internal system

clock, or may be derived from an overflow/

underflow of timer T6 in module GPT2. This

provides a wide range of variation for the timer

period

and

resolution

and

allows

precise

adjustments to application specific requirements.

In addition, external count inputs for CAPCOM

timers T0 and T7 allow event scheduling for the

capture/compare registers relative to external

events.

Each of the two capture/compare register arrays

contain

dual

purpose

capture/compare

registers, each of which may be individually

allocated to either CAPCOM timer T0 or T1 (T7 or

T8, respectively), and programmed for capture or

compare

functions.

Each

has

one

associated port pin which serves as an input pin

for triggering the capture function, or as an output

pin (except for CC24...CC27) to indicate the

occurrence of a compare event.

When a capture/compare register has been

selected for capture mode, the current contents of

the allocated timer will be latched (captured) into

the capture/compare register in response to an

external event at the port pin which is associated

with this register. In addition, a specific interrupt

request for this capture/compare register is

generated. Either a positive, a negative, or both a

positive and a negative external signal transition

at the pin can be selected as the triggering event.

The contents of all registers which have been

selected for one of the five compare modes are

continuously compared with the contents of the

allocated timers. When a match occurs between

the timer value and the value in a capture/

compare register, specific actions will be taken

based on the selected compare mode (see

Table 4).

The input frequencies fTx for Tx are determined as

a function of the CPU clocks. The formulas are

detailed in the user manual. The timer input fre-

quencies, resolution and periods which result

from the selected pre-scaler option in TxI when

using a 25MHz CPU clock are listed in the table

below. The numbers for the timer periods are

based on a reload value of 0000H. Note that some

numbers may be rounded to 3 significant figures

(see Table 5).

Table 4 : Compare modes

Compare Modes

Function

Mode 0

Interrupt-only compare mode ; several compare interrupts per timer period are possible

Mode 1

Pin toggles on each compare match ; several compare events per timer period are possible

Mode 2

Interrupt-only compare mode ; only one compare interrupt per timer period is generated

Mode 3

Pin set ‘1’ on match; pin reset ‘0’ on compare time overflow ; only one compare event per

timer period is generated

Double Register Mode

Two registers operate on one pin; pin toggles on each compare match ; several compare

events per timer period are possible.

Table 5 : CAPCOM timer input frequencies, resolution and periods

fCPU = 25MHz

Timer Input Selection TxI

000B

001B

010B

011B

100B

101B

110B

111B

Pre-scaler for fCPU

128

256

512

1024

Input Frequency

3.125MHz

1.56MHz

781KHz

391KHz

195KHz

97.7KHz

48.8KHz

24.4KHz

Resolution

320ns

640ns

1.28

µs

2.56

µs

5.12

µs

10.24

µs

20.48

µs

40.96

µs

Period

21.0ms

41.9ms

83.9ms

167ms

336ms

671ms

1.34s

2.68s

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