COP685BC datasheet(16/57 Pages) NSC

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Timers (Continued)

TIMER CONTROL FLAGS

The control bits and their functions are summarized below.

T1C3

Timer mode control

T1C2

Timer mode control

T1C1

Timer mode control

T1C0

Timer Start/Stop control in Modes 1 and 2 (Pro-

cessor Independent PWM and External Event

Counter), where 1 = Start, 0 = Stop

Timer Underflow Interrupt Pending Flag in

Mode 3 (Input Capture)

T1PNDA Timer Interrupt Pending Flag

T1ENA

Timer Interrupt Enable Flag

1 = Timer Interrupt Enabled

0 = Timer Interrupt Disabled

T1PNDB Timer Interrupt Pending Flag

T1ENB

Timer Interrupt Enable Flag

1 = Timer Interrupt Enabled

0 = Timer Interrupt Disabled

The timer mode control bits (T1C3, T1C2 and T1C1) are detailed below:

Mode

T1C3

T1C2

T1C1

Description

Interrupt A

Source

Interrupt B

Source

Timer

Counts On

PWM: T1A Toggle

Autoreload RA

Autoreload RB

PWM: No T1A

Toggle

Autoreload RA

Autoreload RB

External Event

Counter

Timer

Underflow

Pos. T1B Edge

Pos. T1A

Edge

External Event

Counter

Timer

Underflow

Pos. T1B Edge

Pos. T1A

Edge

Captures:

Pos. T1A Edge

Pos. T1B Edge

T1A Pos. Edge

or Timer

T1B Pos. Edge

Underflow

Captures:

Pos. T1A

Neg. T1B

T1A Pos. Edge

Edge or Timer

Edge

T1B Neg. Edge

Underflow

Captures:

Neg. T1A

Neg. T1B

T1A Neg. Edge

Edge or Timer

Edge

T1B Neg. Edge

Underflow

Captures:

Neg. T1A

Neg. T1B

T1A Neg. Edge

Edge or Timer

Edge

T1B Neg. Edge

Underflow

HIGH SPEED, CONSTANT RESOLUTION

PWM TIMER

The device has one processor independent PWM timer. The

PWM timer operates in two modes: PWM mode and capture

mode. In PWM mode the timer outputs can be programmed

to two pins PWM0 and PWM1. In capture mode, pin PWM0

functions as the capture input.

Figure 12 shows a block dia-

gram for this timer in capture mode and

Figure 13 shows a

block diagram for the timer in PWM mode.

PWM Timer Registers

The PWM Timer has three registers: PWMCON, the PWM

control register, RLON, the PWM on-time register and

PSCAL, the prescaler register.

PWM Prescaler Register (PSCAL) (Address X’00A0)

The prescaler is the clock source for the counter in both

PWM mode and in frequency monitor mode.

PSCAL is a read/write register that can be used to program

the prescaler. The clock source to the timer in both PWM and

capture modes can be programmed to CKI/N where N =

PSCAL + 1, so the maximum PWM clock frequency = CKI

and the minimum PWM clock frequency = CKI/256. The pro-

cessor is able to modify the PSCAL register regardless of

whether the counter is running or not and the change in fre-

quency occurs with the next underflow of the prescaler (CK-

PWM).

PWM On-time Register (RLON) (Address X’00A1)

RLON is a read/write register. In PWM mode the timer output

will be a “1” for RLON counts out of a total cycle of 255 PWM

clocks. In capture mode it is used to program the threshold

frequency.

The PWM timer is specially designed to have a resolution of

255 PWM clocks. This allows the duty cycle of the PWM out-

put to be selected between 1/255 and 254/255. A value of 0

in the RLON register will result in the PWM output being con-

tinuously low and a value of 255 will result in the PWM output

being continuously high.

Note: The effect of changing the RLON register during active PWM mode op-

eration is delayed until the boundary of a PWM cycle. In capture mode

the effect takes place immediately.

COP685BC Datasheet(PDF) 16 Page - National Semiconductor (TI)

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