COP888GW Datasheet, PDF(13/44 Page) National Semiconductor (TI) – 8-Bit Microcontroller with Pulse Train Generators

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COP888GW Datasheet, PDF (13/44 Pages) National Semiconductor (TI) – 8-Bit Microcontroller with Pulse Train Generators

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Timers (Continued)

TIMER CONTROL FLAGS

The timers T1 and T2 have identical control structures The

control bits and their functions are summarized below

TxC0

Timer Start Stop controI in Modes 1 and 2 (Proc-

essor Independent PWM and External Event

Counter) where 1 e Start 0 e Stop Timer Un-

derfIow Interrupt Pending Flag in Mode 3 (Input

Capture)

TxPNDA Timer Interrupt Pending Flag

TxPNDB Timer Interrupt Pending Flag

TxENA Timer Interrupt Enable FIag

TxENB Timer Interrupt Enable Flag

1 e Timer Interrupt EnabIed

0 e Timer Interrupt Disabled

TxC3 Timer mode controI

TxC2 Timer mode control

TxC1 Timer mode controI

The timer mode controI bits (TxC3 TxC2 and TxC1) are

detailed beIow

Capture Timer

This device contains two independent capture timers Cap-

ture Timer 1 and Capture Timer 2 Each capture timer con-

tains an 8-bit programmable prescaler register a 16-bit

down counter a 16-bit input capture register and capture

edge select Iogic The 16-bit down counter is clocked at a

specific frequency determined by the value loaded into the

prnscaler register A selected positive or negative edge

transition on the capture input causes the contents of the

down counter to be latched into the capture register The

values captured in the registers reflect the eIapsed time be-

tween two positive or two negative transitions on the cap-

ture input The time between a positive and negative edge

(a pulse width) may be measured if the selected capture

edge is switched after the first edge is captured Each cap-

ture timer may be stopped started under software control

and each capture timer may be configured to interrupt the

microcontroller on an underflow or input capture

Figure 10 shows the capture timer 1 block diagram

TABLE II Timer Mode Control

TxC3

TxC2

TxC1

Timer Mode

MODE 2 (External Event Counter)

MODE 1 (PWM) TxA Toggle

MODE 1 (PWM) No TxA Toggle

MODE 3 (Capture) Captures

TxA Positive Edge

TxB Positive Edge

MODE 3 (Capture) Captures

TxA Positive Edge

TxB Negative Edge

MODE 3 (Capture) Captures

TxA Negative Edge

TxB Positive Edge

MODE 3 (Capture) Captures

TxA Negative Edge

TxB Negative Edge

Interrupt A

Source

Timer Underflow

Autoreload RA

Positive TxA Edge or

Timer Underflow

Positive TxA Edge or

Timer Underflow

Negative TxA Edge or

Timer Underflow

Negative TxA Edge or

Timer Underflow

Interrupt B

Source

Positive TxB Edge

Autoreload RB

Positive TxB Edge

Negative TxB Edge

Positive TxB Edge

Negative TxB Edge

Timer

Counts On

TxA Positive Edge

TxA Negative Edge

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