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

FX /FX Series Programmable Controllers
3U 3UC
Programming Manual - Basic & Applied Instruction Edition
4.8.3

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).
Combined two data registers 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
• Data once written to a data register does not change unless another data is written.
When the PLC mode switches from "RUN" to "STOP" or when the power is interrupted, however, all data
stored in general type data registers are 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 the contents even when the PLC mode switches from
"RUN" to "STOP" or when the power is interrupted.
• 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.
M8002
Initial pulse
2. Special type data registers
• Data registers that data for special purpose are written or that specific contents have been written in
advance.
The contents of special type data registers are cleared to the 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 36.
104
→ For the details of each backup method, refer to Section 2.6.
FNC 40
D512 D999
ZRST
FNC 12
K250 D8000
MOV
FNC 07
WDT
→ For the types and functions of special data registers, refer to Chapter 36.
4.8 Data Register and File Register [D]
Data stored in D512 to D999 are
cleared to "0".
→ For file registers, refer to Subsection 4.8.4.
The watchdog timer is set to 250 ms.
The watchdog timer is refreshed.
4 Devices in Detail