ST10 datasheet(20/58 Pages) STMICROELECTRONICS

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ST10F163

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IX - GENERAL PURPOSE TIMER (GPT) UNIT

The GPT unit is a flexible multifunctional timer/

counter structure which is used for time related

tasks such as event timing and counting, pulse

width and duty cycle measurements, pulse gener-

ation, or pulse multiplication. The GPT unit con-

tains five 16-bit timers organized into two separate

modules GPT1 and GPT2. Each timer in each

module may operate independently in several dif-

ferent modes, or may be concatenated with

another timer of the same module.

IX.1 - GPT1

Each of the three timers T2, T3, T4 of module

GPT1 can be configured individually for one of

three basic modes of operation: timer, gated

timer, and counter mode. In Timer Mode, the

input clock for a timer is derived from the CPU

clock, divided by a programmable pre-scaler. In

counter Mode a timer is clocked in reference to

external events. Gated timer mode supports pulse

width or duty cycle measurement, where the oper-

ation of a timer is controlled by the ‘gate’ level on

an external input pin. Each timer has one associ-

ated port pin (TxIN) which serves as gate or clock

input.

Table 8 lists the timer input frequencies, resolution

and periods for each pre-scaler option at 25 MHz

CPU clock (see Table 8).

The count direction (up/down) for each timer is

programmable by software or is altered dynami-

cally by an external signal on a port pin (TxEUD).

For example, this facilitates position tracking.

Timer T3 has output toggle latches (TxOTL) which

changes state on each timer over-flow/underflow.

The state of this latch may be output on port pins

(TxOUT) e. g. for time out monitoring of external

hardware components, or may be used internally

to clock timers T2 and T4 for measuring long time

periods with high resolution.

In addition to their basic operating modes, timers

T2 and T4 may be configured as reload or capture

registers for timer T3. When used as reload or

capture registers, timers T2 and T4 are stopped.

The content of timer T3 is captured into T2 or T4

in response to a signal at their associated input

pins (TxIN). Timer T3 is reloaded with the con-

tents of T2 or T4, triggered, either by an external

signal or by a selectable state transition of its tog-

gle latch, T3OTL. When both T2 and T4 are con-

figured to alternately reload T3 on opposite state

transitions of T3OTL with the low and high times

of a PWM signal, this signal can be constantly

generated without software intervention.

IX.2 - GPT2

The GPT2 module provides precise event control

and time measurement. It includes two timers (T5,

T6) and a capture/reload register (CAPREL). Both

timers can be clocked with an input clock which is

derived from the CPU clock via a programmable

prescaler or with external signals. The count

direction (up/down) for each timer is programma-

ble by software or may additionally be altered

dynamically by an external signal on a port pin

(TxEUD). Concatenation of the timers is sup-

ported via the output toggle latch (T6OTL) of timer

T6 which changes its state on each timer over-

flow/underflow.

The state of this latch may be used to clock timer

T5, or it may be output on a port pin (T6OUT). The

overflows/underflows of timer T6 can additionally

be used to clock the CAPCOM timers T0 or T1,

and to cause a reload from the CAPREL register.

The CAPREL register may capture the contents of

timer T5 based on an external signal transition on

the corresponding port pin (CAPIN), and timer T5

may optionally be cleared after the capture proce-

dure. This allows absolute time differences to be

measured or pulse multiplication to be performed

without software overhead.

Table 9 lists the timer input frequencies, resolution

and periods for each pre-scaler option at 25 MHz

CPU clock.

Table 8 : GPT1 timer input frequencies, resolution and periods

fCPU = 25MHz

Timer Inpu t Selection T2I / T3I / T4I

000B

001B

010B

011B

100B

101B

110B

111B

Pre-scaler factor

128

256

512

1024

Input Frequency

3.125MHz

1.563MHz

781.3kHz

390.6kHz

195.3kHz

97.66kHz

48.83kHz

24.41kHz

Resolution

320 ns

640 ns

128 ns

2.56

µs

5.12

µs

10.24

µs

20.48

µs

40.96

µs

Period

21.0 ms

41.9 ms

83.9 ms

167 ms

336 ms

671 ms

1.34 s

2.68 s

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