What is the difference between M relays and I/Q relays in IDEC WindLDR?

I relays map to physical input terminals. Q relays map to physical output terminals. M relays are internal memory bits with no physical connection, used for intermediate logic and flags.

How many timers does the IDEC FC6A support?

The FC6A supports up to 1,024 timer instructions (T0-T1023) in WindLDR with 10ms or 100ms resolution.

IDEC WindLDR Ladder Logic Basics

Quick Answer

Ladder logic is the primary programming language for IDEC FC6A PLCs. WindLDR provides a graphical ladder editor with contacts, coils, timers, counters, comparison, math, and data move instructions. Programs use IDEC memory types: I (input), Q (output), M (internal relay), R (data register), T (timer), and C (counter).

IDEC Memory Types in Ladder

I — Physical input relays mapped to input terminals
Q — Physical output relays mapped to output terminals
M — Internal memory relays for intermediate logic and flags
R — Data registers (16-bit words) for numeric values
T — Timer instructions with accumulated values
C — Counter instructions with accumulated values

Contacts and Coils

Normally Open (NO) — Passes continuity when the referenced bit is ON (true)
Normally Closed (NC) — Passes continuity when the referenced bit is OFF (false)
Output Coil — Sets the output ON when the rung is true, OFF when false
Set Coil — Latches the output ON; stays ON until explicitly reset
Reset Coil — Resets a latched output to OFF

Timer Instructions

TMR (On-Delay Timer) — Output activates after the input has been ON for the preset time
TMROF (Off-Delay Timer) — Output stays ON for the preset time after the input goes OFF
TMRSS (One-Shot Timer) — Output pulses for the preset time on a rising edge of the input

Counter Instructions

CNT (Up Counter) — Increments on each rising edge of the count input. Output activates when the accumulated value reaches the preset.
CNTD (Up/Down Counter) — Counts up or down based on separate input signals

Comparison and Math Instructions

Comparison instructions (CMP, =, ≠, >, <, ≥, ≤) test R register values against constants or other registers. Math instructions (ADD, SUB, MUL, DIV) perform arithmetic on R register values. The MOV instruction copies values between registers.

Example: Motor Start/Stop with Seal-In

Rung 0: [NO I0] --+-- [Coil Q0]     (Start PB → Motor)
                   |
        [NO Q0] --+                  (Seal-in)
        [NC I1] ----                 (Stop PB, NC)
Rung 1: [NC I2] ---- [Coil Q0 RST]  (Overload → Reset motor)

Example: Timed Fill Cycle

Rung 0: [NO I0] ---- [TMR T0 K300]  (Start → 30-second timer)
Rung 1: [NO T0] ---- [Coil Q1]      (Timer done → Open fill valve)