COPCH940C datasheet(16/26 Pages) NSC

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Functional Description (Continued)

MODE 1. TIMER WITH AUTO-LOAD REGISTER

In this mode of operation, the timer T1 counts down at the in-

struction cycle rate. Upon underflow the value in the register

R1 gets automatically reloaded into the timer which contin-

ues to count down. The timer underflow can be programmed

to interrupt the microcontroller. A bit in the control register

CNTRL enables the TIO (G3) pin to toggle upon timer under-

flows. This allow the generation of square-wave outputs or

pulse width modulated outputs under software control. (See

Figure 8)

MODE 2. EXTERNAL COUNTER

In this mode, the timer T1 becomes a 16-bit external event

counter. The counter counts down upon an edge on the TIO

pin. Control bits in the register CNTRL program the counter

to decrement either on a positive edge or on a negative

edge. Upon underflow the contents of the register R1 are au-

tomatically copied into the counter. The underflow can also

be programmed to generate an interrupt. (See

Figure 8)

MODE 3. TIMER WITH CAPTURE REGISTER

Timer T1 can be used to precisely measure external fre-

quencies or events in this mode of operation. The timer T1

counts down at the instruction cycle rate. Upon the occur-

rence of a specified edge on the TIO pin the contents of the

timer T1 are copied into the register R1. Bits in the control

as a positive edge or as a negative edge. In this mode the

user can elect to be interrupted on the specified trigger edge.

(See

Figure 9.)

TABLE 5. Timer Operating Modes

CNTRL

Bits

765

Operation Mode

T Interrupt

Timer

Counts

0 0 0

External Counter W/Auto-Load Reg.

Timer Underflow

TIO Pos. Edge

0 0 1

External Counter W/Auto-Load Reg.

Timer Underflow

TIO Neg. Edge

0 1 0

Not Allowed

0 1 1

Not Allowed

1 0 0

Timer W/Auto-Load Reg.

Timer Underflow

1 0 1

Timer W/Auto-Load Reg./Toggle TIO Out

Timer Underflow

1 1 0

Timer W/Capture Register

TIO Pos. Edge

1 1 1

Timer W/Capture Register

TIO Neg. Edge

DS009103-13

FIGURE 7. MICROWIRE/PLUS Application

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