Hitachi NJI-350B manual Operation of PWM Output

Chapter 8 High-speed counter, PWM / Pulse train output and Analogue I/O

8.4 PWM Output

A PWM output can be set as an output by setting the operation mode and output terminal. By setting an output to a PWM output, a pulse with a duty ratio in the range that corresponds to the specified frequency can be output.

8.4.1 Operation of PWM Output

The PWM output settings are stored in the special internal outputs. It is only possible to perform the settings through the special internal output when the CPU is stopped and the output is turned off. Once all the input/output settings are completed, the setting of each PWM output can be changed using the special internal outputs for individual setting, regardless of whether the CPU is operating or stopped. In addition, the settings can be changed by a program using the FUN instruction (FUN148). See the chapter about the FUN instruction for information about how to use the FUN instruction for setting.

(1)Basic operation

The special internal outputs R7FC to R7FF are used to control the output. When these special internal outputs are turned on, a pulse is output at the frequency and the on-duty set in the special internal outputs (WRF072 to 79). When the special internal output for output control is turned off, the PWM output is also turned off. The special internal outputs R7FC to R7FF correspond to PWM outputs 1 to 4 (Y100 to Y103); for example, if R7FD is turned on, a pulse train is output from PWM output 2 (Y101). The on/off status of the PWM outputs is not stored in the data memory. Therefore, the status of the terminals used for PWM output monitored by peripheral units, etc. may be different from the actual status of the PWM output terminals.

When a fatal or serious error occurs in the CPU, there will be no output. The output is also stopped if a fatal or serious error occurs in the CPU during output.

R7FC to R7FF

Frequency

On duty

t

Output pulse

Figure 8.25 Basic operation of PWM output

(2)Operation when setting values are changed

The settings of each PWM output (frequency and on-duty) can be changed by the FUN instruction or the special internal outputs (WRF072 to 79) regardless of whether the CPU is operating or stopped.

R7FC to R7FF

Change in both frequency and On duty

Change in On duty	Change in
Frequency	frequency
On duty
	t

Output pulse

Figure 8.26 Operation of PWM output when setting values are changed.

(3)Operation at abnormal settings

The PWM output is not output if the on-duty is set to a value other than the range in use. However, the FUN instruction does not execute setting change when the setting value is abnormal.

R7FC to R7FF

On-duty setting value:	On-duty setting value:
exceeding the range	within the range

Frequency
On duty
		t
Output pulse	Abnormal
Normal settings	settings	Normal settings

Figure 8.27 Operation of PWM output at abnormal settings

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