Mitsubishi Electric MELSEC FX3U Programming Manual page 628

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition
2. High speed counter current value update timing and the effect of DHCMOV instruction
1) High speed counter current value update timing
When a pulse is input to an input terminal for a high speed counter (C235 to C255), the high speed
counter executes up-counting or down-counting.
If the current value of a high speed counter is handled in an applied instruction such as the normal MOV
instruction, the current value is updated at the timing shown in the table below. As a result, it is affected
by the program scan time.
Hardware counter
Software counter
By using DHCMOV instruction, the current value can be updated and transferred when it is executed.
2) Effect of DHCMOV instruction
• By using both input interrupt and DHCMOV instruction, the current value of a high speed counter can
be received at the rising edge or falling edge of an external input (at reception of input interrupt).
• When DHCMOV instruction is used just before a comparison instruction (CMP, ZCP or comparison
contact instruction), the latest value of a high speed counter is used in comparison.The following points
must be kept in mind when using the DHCMOV command.
- When the current value of a high speed counter is compared using CMP, ZCP or comparison
contact instruction (not using a designated high speed counter comparison instruction), a hardware
counter does not change into a software counter.
- When the number of high speed software counter comparison instructions is reduced, the total
frequency limitation is decreased.
- When it is necessary to execute comparison and change an output contact (Y) as soon as the
current value of a high speed counter changes, use a desighnated high speed counter comparison
instruction (HSCS, HSCR or HSZ).
- DHCMOV instruction can be used as many times as necessary.
626
When OUT instruction for the counter is executed
Every time a pulse is input
→ For the condition in which a hardware counter is handled as a software counter,
→ For the limitation in software counters by the total frequency,
24.5 FNC189 – HCMOV / High Speed Counter Move
Current value update timing
→ Refer to the Program example 2.
24 Others – FNC181 to FNC189
refer to Subsection 4.7.9.
refer to Subsection 4.7.10.