National CP3BT26 User Manual
www.national.com
196
CP3BT26
26.0 Multi-Function Timer
The Multi-Function Timer module contains a pair of 16-bit
timer/counters. Each timer/counter unit offers a choice of
clock sources for operation and can be configured to oper-
ate in any of the following modes:
timer/counters. Each timer/counter unit offers a choice of
clock sources for operation and can be configured to oper-
ate in any of the following modes:
Processor-Independent Pulse Width Modulation (PWM)
mode, which generates pulses of a specified width and
duty cycle, and which also provides a general-purpose
timer/counter.
duty cycle, and which also provides a general-purpose
timer/counter.
Dual-Input Capture mode, which measures the elapsed
time between occurrences of external events, and which
also provides a general-purpose timer/counter.
also provides a general-purpose timer/counter.
Dual Independent Timer mode, which generates system
timing signals or counts occurrences of external events.
Single-Input Capture and Single Timer mode, which pro-
vides one external event counter and one system timer.
The timer unit uses two I/O pins, called TA and TB. The tim-
er I/O pins are alternate functions of the PG7 and PE4 port
pins, respectively.
er I/O pins are alternate functions of the PG7 and PE4 port
pins, respectively.
26.1
TIMER STRUCTURE
Figure 97 is a block diagram showing the internal structure
of the MFT. There are two main functional blocks: a Timer/
Counter and Action block and a Clock Source block. The
Timer/Counter and Action block contains two separate tim-
er/counter units, called Timer/Counter 1 and Timer/Counter
2.
of the MFT. There are two main functional blocks: a Timer/
Counter and Action block and a Clock Source block. The
Timer/Counter and Action block contains two separate tim-
er/counter units, called Timer/Counter 1 and Timer/Counter
2.
Figure 97.
Multi-Function Timer Block Diagram
26.1.1
Timer/Counter Block
The Timer/Counter block contains the following functional
blocks:
blocks:
Two 16-bit counters, Timer/Counter 1 (TCNT1) and Tim-
er/Counter 2 (TCNT2)
Two 16-bit reload/capture registers, TCRA and TCRB
Control logic necessary to configure the timer to operate
Control logic necessary to configure the timer to operate
in any of the four operating modes
Interrupt control and I/O control logic
In a power-saving mode that uses the low-frequency
(32.768 kHz) clock as the System Clock, the synchroniza-
tion circuit requires that the Slow Clock operate at no more
than one-fourth the speed of the 32.768 kHz System Clock.
(32.768 kHz) clock as the System Clock, the synchroniza-
tion circuit requires that the Slow Clock operate at no more
than one-fourth the speed of the 32.768 kHz System Clock.
26.1.2
Clock Source Block
The Clock Source block generates the signals used to clock
the two timer/counter registers. The internal structure of the
Clock Source block is shown in Figure 98.
the two timer/counter registers. The internal structure of the
Clock Source block is shown in Figure 98.
Figure 98.
Multi-Function Timer Clock Source
Reload/Capture A
TCRA
Timer/Counter
Clock Source
Action
TA
Interrupt B
Interrupt A
T
oggle/Capture/Interr
upt
Cloc
k Prescaler/Selector
Timer/Counter 1
TCNT1
Reload/Capture B
TCRB
Timer/Counter 2
TCNT2
PWM/Capture/Counter
Mode Select + Control
External Event
System
Clock
TB
DS081
Counter 1
Clock
Select
Counter 1
Clock
Clock
Counter 2
Clock
Select
Counter 2
Clock
Clock
Synchr.
External Event
Pulse Accumulator
5-Bit
Prescaler Counter
Prescaler Register
TPRSC
Reset
System
Clock
TB
Prescaled Clock
No Clock
DS082