COP820CJ datasheet(19/35 Pages) NSC

19 / 35 page

Modulator/Timer (Continued)

b. Variable Duty Cycle:

When MC3 = 0 and MC2 = 1, a variable duty cycle PWM sig-

nal is generated on the L7 output pin. The counter is clocked

by tC. In this mode the 16-bit timer T1 along with the 8-bit

down counter are used to generate a variable duty cycle

PWM signal. The timer T1 underflow sets MC1 which starts

the down counter and it also sets L7 high (L7 should be con-

figured as an output).When the counter underflows the MC1

control bit is reset and the L7 output will go low until the next

timer T1 underflow. Therefore, the width of the output pulse

is controlled by the 8-bit counter and the pulse duration is

controlled by the 16-bit timer T1 (

Figure 15). Timer T1 must

be configured in “PWM Mode/Toggle TIO Out” (CNTRL1 Bits

7,6,5 = 101).

Table 8 shows the different operation modes for the

Modulator/Timer.

TABLE 8. Modulator/Timer Modes

Control Bits in

Operation Mode

L7 Function

CNTRL2(00CC)

MC3

MC2

MC1

Normal I/O

50% Duty Cycle Mode (Clocked by

Variable Duty Cycle Mode (Clocked

by t

c) Using Timer 1 Underflow

Modulator Mode (Clocked by t

Modulator Mode (Clocked by CKI)

Note 11: MC1, MC2 and MC3 control bits are cleared upon reset.

Internal Data Bus

DS011208-16

FIGURE 13. Mode 1: Modulator Block Diagram/Output Waveform

DS011208-17

COP820CJ Datasheet(PDF) 19 Page - National Semiconductor (TI)