414
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
15 External FX I/O Device – FNC 70 to FNC 79
15.5 FNC 74 – SEGL / Seven Segment With Latch
15.5.1
How to select a seven-segment display unit
When selecting a seven-segment display unit based on its electrical characteristics, refer to the manual
below:
→
For the wiring, refer to the Hardware Manual of the used PLC.
1. Points to be checked for the seven-segment specifications
1) Whether the input voltage and current characteristics of the data input and strobe signal satisfy the output
specifications of the PLC.
- Whether the input signal voltage (Lo) is approximately 1.5 V or less
- Whether the input voltage is from 5V DC to 30V DC
2) Whether the seven-segment display unit has the BCD decoding and latch functions
15.5.2
How to select parameter "n" based on seven-segment display specifications
The value set to the parameter "n" varies depending on the signal logic of the seven-segment display. Select
"n" as described below.
The check column is provided at the bottom of the table. Check a corresponding type of logic (positive or
negative), and utilize it for parameter setting.
1. Role of the parameter "n"
The parameter "n" should be determined according to the data input logic (positive or negative) of the seven-
segment display unit, the logic (positive or negative) of the strobe signal and the number of sets of 4 digits to
be controlled (1 or 2).
2. Checking the output logic of the PLC
Transistor outputs in PLCs are classified into the sink output type and source output type. The table below
shows the specifications for each type.
Logic
Negative logic
Positive logic
Product type
FX
3UC
-32MT-LT, FX
3U
PLC
(output extension equipment)
FX
3U
PLC (output extension equipment)
Output type
Sink output (
−
common)
Source output (+ common)
Output circuit
Description
Because transistor output (sink) is provided, the
output becomes low level (0 V) when the internal
logic is "1 (ON output)". This is called "negative
logic."
Because transistor output (source) is provided, the
output becomes high level (V+) when the internal
logic is "1 (ON output)". This is called "positive
logic."
Check
ON
PLC
LOW
Logic 1
Pull-up
resistor
COM1
Y000
ON
PLC
Logic 1
Pull-
down
resistor
V+
HIGH
COM1
Y000