COP688CL datasheet(18/40 Pages) NSC

18 / 40 page

Timers (Continued)

The timer mode control bits (TxC3 TxC2 and TxC1) are detailed below

TxC3

TxC2

TxC1

Timer Mode

Interrupt A

Interrupt B

Timer

Source

Counts On

MODE 2 (External

Timer

Pos TxB

TxA

Event Counter)

Underflow

Edge

Pos Edge

MODE 2 (External

Timer

Pos TxB

TxA

Event Counter)

Underflow

Edge

Neg Edge

MODE 1 (PWM)

Autoreload

TxA Toggle

MODE 1 (PWM)

Autoreload

No TxA Toggle

MODE 3 (Capture)

Pos TxA

Pos TxB

Captures

Edge or

Edge

TxA Pos Edge

Timer

TxB Pos Edge

Underflow

MODE 3 (Capture)

Pos TxA

Neg TxB

Captures

Edge or

Edge

TxA Pos Edge

Timer

TxB Neg Edge

Underflow

MODE 3 (Capture)

Neg TxB

Pos TxB

Captures

Edge or

Edge

TxA Neg Edge

Timer

TxB Pos Edge

Underflow

MODE 3 (Capture)

Neg TxA

Neg TxB

Captures

Edge or

Edge

TxA Neg Edge

Timer

TxB Neg Edge

Underflow

Power Save Modes

The device offers the user two power save modes of opera-

tion HALT and IDLE In the HALT mode all microcontroller

activities are stopped In the IDLE mode the on-board oscil-

lator circuitry and timer T0 are active but all other microcon-

troller activities are stopped In either mode all on-board

RAM registers IO states and timers (with the exception of

T0) are unaltered

HALT MODE

The device is placed in the HALT mode by writing a ‘‘1’’ to

the HALT flag (G7 data bit) All microcontroller activities

including the clock timers are stopped The WATCHDOG

logic is disabled during the HALT mode However the clock

monitor circuitry if enabled remains active and will cause

the WATCHDOG output pin (WDOUT) to go low If the

HALT mode is used and the user does not want to activate

the WDOUT pin the Clock Monitor should be disabled after

the device comes out of reset (resetting the Clock Monitor

control bit with the first write to the WDSVR register) In the

HALT mode the power requirements of the device are mini-

mal and the applied voltage (VCC) may be decreased to Vr

(Vr e 20V) without altering the state of the machine

The device supports three different ways of exiting the

HALT mode The first method of exiting the HALT mode is

with the Multi-Input Wakeup feature on the L port The sec-

ond method is with a low to high transition on the CKO (G7)

pin This method precludes the use of the crystal clock con-

figuration (since CKO becomes a dedicated output) and so

may be used with an RC clock configuration The third

method of exiting the HALT mode is by pulling the RESET

pin low

Since a crystal or ceramic resonator may be selected as the

oscillator the Wakeup signal is not allowed to start the chip

running immediately since crystal oscillators and ceramic

resonators have a delayed start up time to reach full ampli-

tude and frequency stability The IDLE timer is used to gen-

erate a fixed delay to ensure that the oscillator has indeed

stabilized before allowing instruction execution In this case

upon detecting a valid Wakeup signal only the oscillator

circuitry is enabled The IDLE timer is loaded with a value of

256 and is clocked with the tc instruction cycle clock The tc

clock is derived by dividing the oscillator clock down by a

factor of 10 The Schmitt trigger following the CKI inverter

on the chip ensures that the IDLE timer is clocked only

when the oscillator has a sufficiently large amplitude to

meet the Schmitt trigger specifications This Schmitt trigger

is not part of the oscillator closed loop The startup timeout

from the IDLE timer enables the clock signals to be routed

to the rest of the chip

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COP688CL Datasheet(PDF) 18 Page - National Semiconductor (TI)

COP688CL Datasheet(HTML) 18 Page - National Semiconductor (TI)

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