Functions And Operation Examples Of Data Registers - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
4.9.3

Functions and operation examples of data registers

Data registers are devices for storing numeric data.
Each data register stores 16-bit data (whose most significant bit specifies the positive or negative sign). Two
data registers combined can store 32-bit numeric data (whose most significant bit specifies the positive or
negative sign).
1. General type and latched (battery backed) type data registers
• Once data is written to a data register it does not change unless other data overwrite it.
When the PLC mode switches from "RUN" to "STOP" or when the power is interrupted, however, all data
stored in general type data registers is cleared to "0".
If the special auxiliary relay M8033 has been driven in advance, data is held even when the PLC mode
switches from "RUN" to "STOP".
• Latched (battery backed) type data registers hold their contents even when the PLC mode switches from
"RUN" to "STOP" or when the power is interrupted.
In FX /FX
3U 3UC
In FX PLCs, the contents of data registers are backed up by the EEPROM built into the PLC. When the
3G
optional battery is installed, the battery backs up the contents of some general type data registers against
power failure.
The contents of data registers are backed up by the battery built in the PLC.
• When using fixed latched (battery backed) type data registers as general type data registers, provide the
following reset circuit by RST or ZRST instruction at the head step in a program.
Ex. FX /FX
3U 3UC
M8002
Initial pulse
2. Special type data registers
• Special type data registers contain informative, special purpose data and are sometimes written to during
program operation.
The contents of special type data registers are cleared to their initial values when restoring the power.
(Generally, these data registers are cleared to "0" at first, and then the initial values (if there are any) are
written by the system ROM.)
• For example, the watchdog timer time is set initially to D8000 by the system ROM. When changing the
contents, write a desired time to D8000 by transfer instruction MOV (FNC 12).
M8002
Initial pulse
→ For the data backup characteristics of special data registers, refer to Section 2.6 and Chapter 37.
PLCs, the contents of data registers are backed up by the battery built into the PLC.
PLCs
FNC 40
D512
ZRST
FNC 12
K250
MOV
FNC 07
WDT
→ For the types and functions of special data registers, refer to Chapter 37.
→ For details on each backup method, refer to Section 2.6.
Data stored in D512 to D999 are
D999
cleared to "0".
→ For file registers, refer to Subsection 4.8.4.
The watchdog timer is set to 250 ms.
D8000
The watchdog timer is refreshed.
4 Devices in Detail
4.9 Data Register and File Register [D]
1
2
3
4
5
6
7
8
9
10
133