cp3ub17 National Semiconductor Corporation, cp3ub17 Datasheet - Page 136

• Manufacturer Part Number: cp3ub17
• Description: Reprogrammable Connectivity Processor With Usb Interface
• Manufacturer: National Semiconductor Corporation

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22.0 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:
22.1.1
The Timer/Counter block contains the following functional
blocks:
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.
Input Capture mode, which measures the elapsed time
between occurrences of external events, and which also
provides a general-purpose timer/counter.
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
in any of the four operating modes
Interrupt control and I/O control logic
Timer/Counter Block
System
Reset
Clock
System
Clock
Prescaler Register
Prescaler Counter
Clock Source
TPRSC
Figure 48. Multi-Function Timer Block Diagram
5-Bit
Figure 49. Multi-Function Timer Clock Source
External Event
Prescaled Clock
No Clock
Reload/Capture A
Reload/Capture B
Timer/Counter 1
Timer/Counter 2
Timer/Counter
PWM/Capture/Counter
Mode Select + Control
TCNT1
TCNT2
TCRA
TCRB
136
The timer unit uses an I/O pin called TA, which is an alter-
nate function of the PI7 port pin.
22.1
Figure 48 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.
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.
22.1.2
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 49.
Dual Independent Timer mode, which generates system
timing signals.
Action
TIMER STRUCTURE
Clock Source Block
Interrupt A
Interrupt B
Counter 1
Counter 2
Select
Select
Clock
Clock
DS165
TA
Counter 1
Clock
Counter 2
Clock
DS164