On-Demand Function - Mitsubishi FX3U-USB-BD User Manual

FX Series PLC User's Manual - Data Communication Edition
Computer Link
7.13

On-demand Function

When there is data to be sent from a PLC to the computer, the on-demand function can specify the data
register area storing the data to be sent, and let the PLC start sending.
When data is sent between the computer and a PLC, only the computer can start data transmission.
When there is emergency data to be sent from a PLC to the computer, the on-demand function is applicable
to let the PLC begin sending data to the computer.
Important point
This function is applicable when the computer and the PLC CPU have the 1-to-1 configuration.
7.13.1 Special data registers and special auxiliary relays used in on-demand function
The tables below show the special data registers and special auxiliary relays used in the on-demand function.
1. In all PLCs except FX
FX PLCs
3UC
Device
On-demand send
*1
M8127
processing
M8128 On-demand error flag
On-demand byte/word
M8129
changeover
On-demand head device
D8127
number specification
On-demand data quantity
D8128
specification
*1. FX , FX
0N
D-74
PLC
D8127
D8128
Sequence
D(n)
program
D(n+m-1)
, FX and FX
3G 3U
Name
Remains ON while the on-demand function is being executed.
ON: On-demand data is being sent.
OFF: Sending of on-demand data is completed.
Turns ON when an error is included in a specified value to be sent in the on-
demand function.
ON: Error is included.
OFF: Error is not included.
Specifies the unit (byte or word) of data handled in the on-demand function.
ON: Unit = Byte (8-bit)
OFF: Unit = Word (16-bit)
Sets the head data register device number containing the data to be sent
using the on-demand function in a sequence program.
Sets the amount of data to be sent using the on-demand function in a
sequence program.
, FX and FX PLCs do not support this device.
1S 1N 1NC
Head device number (n)
Data length (m)
PLCs and when ch1 is used in FX
3UC
Description
7 Commands
7.13 On-demand Function
Computer
, FX and
3G 3U