Hitachi NJI-350B manual Pulse Train Output, Operation of Pulse Output

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

8.5 Pulse Train Output

A pulse output can be assigned to an output by setting an output terminal. By setting an output to pulse output, a specified number of consecutive pulses with a duty ratio of 30 to 70 % can be output. ((To output a pulse having a duty ratio of 50 %, set the value corresponding to the CPU model in the special internal output WRF06B, by referring to Section 8.1.4.) A minimum of 10 Hz to a maximum of 5 kHz can be specified as frequency values. (The maximum frequency of 5 kHz represents the total of all pulse output frequencies.)

8.5.1 Operation of Pulse Output

The settings of the pulse outputs 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 chain output can be changed using the special internal outputs for individual setting, regardless of whether the CPU is operating or stopped. In addition, by using the FUN instruction, settings can be changed by a program (FUN150), or pulse outputs with the acceleration/deceleration function can be generated (FUN151). Refer to 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 train is output at the frequency set in the special internal outputs (WRF072 to 7D) for the set number of pulses. After the set number of pulses is output, the special internal outputs R7FC to R7FF for output control are turned off by the system. The special internal outputs R7FC to R7FF correspond to pulse outputs 1 to 4 (Y100 to Y103); for example, if R7FD is turned on, a pulse is output from pulse output 2 (Y101). If peripheral units, etc. forcefully turn these special internal outputs off, the pulse output is turned off even if the set number of pulses has not yet been output. The on/off status of the PWM output is not stored in the data memory. Therefore, the status of the terminals used for pulse output monitored by peripheral units, etc. may be different from the actual status of the pulse 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 to the CPU during output.

In addition, pulses are not output while the backup memory is being written (R7EF=1). Therefore, care should be taken when handling the pulse output immediately after a program transfer or after a program change while running.

Number of output pulses 2

Pulse output Pulse output Pulse output

R7FC to R7FF	Turned off by	Forcefully	Turned off by
Frequency	the system	turned off	the system
Frequency/2
			t

Output pulse

Figure 8.31 Basic operation of pulse output

(2)Operation when setting values are changed

The settings of the pulse outputs (frequency and number of output pulses) can be changed by the FUN instruction or the special internal outputs (WRF072 to 7D) regardless of whether the CPU is operating or stopped. If the settings are made during the execution of a program in such way that the total frequency of all the pulse outputs exceeds 5 kHz, the frequency settings will not be changed. Also, the corresponding bit in the abnormality display special internal output is turned on, and the output will continue to operate at the previously set frequency. (The setting value of the special internal output also returns to the value set before the abnormal setting was made.)

R7FC to R7FF	Frequency change	Frequency
		change	Frequency
				Frequency
			change (set to	change
Frequency			exceed 5 kHz)
Frequency/2
				t

Output pulse

In case the frequency becomes 5 kHz or more, the previous setting value is used for operation.

Figure 8.32 Operation when the pulse output frequency is changed

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