I2CCON datasheet(88/210 Pages) MICROCHIP

88 / 210 page

dsPIC30F2011/2012/3012/3013

DS70139G-page 88

12.1

Timer2 and Timer3 Selection Mode

Each output compare channel can select between one

of two 16-bit timers, Timer2 or Timer3.

The selection of the timers is controlled by the OCTSEL

bit (OCxCON<3>). Timer2 is the default timer resource

for the output compare module.

12.2

Simple Output Compare Match

Mode

When control bits OCM<2:0> (OCxCON<2:0>) = 001,

010

or 011, the selected output compare channel is

configured for one of three simple Output Compare

Match modes:

• Compare forces I/O pin low

• Compare forces I/O pin high

• Compare toggles I/O pin

The OCxR register is used in these modes. The OCxR

selected incrementing timer count. When a compare

occurs, one of these Compare Match modes occurs. If

the counter resets to zero before reaching the value in

OCxR, the state of the OCx pin remains unchanged.

12.3

Dual Output Compare Match Mode

When control bits OCM<2:0> (OCxCON<2:0>) = 100

or 101, the selected output compare channel is

configured for one of two Dual Output Compare modes,

which are:

• Single Output Pulse mode

• Continuous Output Pulse mode

12.3.1

SINGLE PULSE MODE

For the user to configure the module for the generation

of a single output pulse, the following steps are

required (assuming timer is off):

• Determine instruction cycle time TCY.

• Calculate desired pulse width value based on TCY.

• Calculate time to start pulse from timer start value

of 0x0000.

• Write pulse width start and stop times into OCxR

and OCxRS Compare registers (x denotes

channel 1 to N).

• Set Timer Period register to value equal to or

greater than value in OCxRS Compare register.

• Set OCM<2:0> = 100.

• Enable timer, TON bit (TxCON<15>) = 1.

To initiate another single pulse, issue another write to

set OCM<2:0> = 100.

12.3.2

CONTINUOUS PULSE MODE

For the user to configure the module for the generation

of a continuous stream of output pulses, the following

steps are required:

• Determine instruction cycle time TCY.

• Calculate desired pulse value based on TCY.

• Calculate timer to start pulse width from timer start

value of 0x0000.

• Write pulse width start and stop times into OCxR

and OCxRS (x denotes channel 1 to N) Compare

registers, respectively.

• Set Timer Period register to value equal to or

greater than value in OCxRS Compare register.

• Set OCM<2:0> = 101.

• Enable timer, TON bit (TxCON<15>) = 1.

12.4

Simple PWM Mode

When control bits OCM<2:0> (OCxCON<2:0>) = 110

or 111, the selected output compare channel is

configured for the PWM mode of operation. When

configured for the PWM mode of operation, OCxR is

the main latch (read-only) and OCxRS is the secondary

latch. This enables glitchless PWM transitions.

The user must perform the following steps in order to

configure the output compare module for PWM

operation:

Set the PWM period by writing to the appropriate

period register.

Set the PWM duty cycle by writing to the OCxRS

Configure the output compare module for PWM

operation.

Set the TMRx prescale value and enable the

Timer, TON bit (TxCON<15>) = 1.

12.4.1

INPUT PIN FAULT PROTECTION

FOR PWM

When control bits OCM<2:0> (OCxCON<2:0>) = 111,

the

selected

output

compare

channel

again

configured for the PWM mode of operation with the

additional feature of input Fault protection. While in this

mode, if a logic ‘0’ is detected on the OCFA/B pin, the

respective PWM output pin is placed in the high

impedance input state. The OCFLT bit (OCxCON<4>)

indicates whether a Fault condition has occurred. This

state is maintained until both of the following events

have occurred:

• The external Fault condition has been removed.

• The PWM mode has been re-enabled by writing

to the appropriate control bits.

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