Mitsubishi PLC's internal register Daquan - Database & Sql Blog Articles

During a scan operation, the counter tracks signals from internal components such as X, Y, M, S, T, and C. When the count reaches the preset value, the counter contact activates to control the system and perform the required function. A low-speed counter can not only capture switching signals from input terminals (input relays) but also monitor internal component contacts within the PLC.

Internal counters are categorized based on the frequency of the signals they process, typically divided into low-speed and high-speed counters.

1) Low-Speed Counter

There are four main types:

- 16-bit universal up counter: C0 to C99 (100 points); set value range is K1 to K32767

- 16-bit power-off keep increment counter: C100 to C199 (100 points); set value range is K1 to K32767

- 32-bit universal up/down bidirectional counter: C200 to C219 (20 points); set value range is K-2147483648 to +214783648

- 32-bit power failure keep up/down bidirectional counter: C220 to C234 (15 points); set value range is K-2147483648 to +214783648

2) High-Speed Counter (C)

High-speed counters are designed to process external signals received through input terminals, with frequencies reaching several kilohertz. They can also be reset directly via an input terminal.

The high-speed counter numbers range from C235 to C255, which are all 32-bit up/down bidirectional counters. The counting direction is determined by a special auxiliary relay or an input terminal. The set value range is K-2147483648 to +214783648.

High-speed counters are generally classified into four categories:

- 1-phase no start/reset terminal: C235 to C240

- 1-phase bidirectional: C246 to C250

- 2-phase A-B phase type: C251 to C255

The convention between the high-speed counter and the input terminal (input relay) is as follows:

Note: U = Up counting input; D = Down counting input; A = A phase input; B = B phase input; R = Reset input; S = Start input.

High-speed counters operate using interrupts, making them independent of the scan cycle. The coil of the selected counter must remain active to ensure the counter and its inputs are continuously operational. No other high-speed processing can use the same input terminals during this time.

(1) 1-phase high-speed counter C235 to C240

These counters have a setting range of -2147483648 to +214783648. C241 to C245 include start and reset terminals.

Description:

When the count increases and reaches the set value, the contact changes and remains in that state. When counting down, the count resets.

The counting direction of the 1-phase counter depends on the corresponding flag M8â–¡â–¡â–¡, where â–¡â–¡â–¡ corresponds to the counter number C235 to C245.

(2) 1-phase bidirectional high-speed counter C246 to C250

This type of counter has one input for up-counting and another for down-counting. It requires separate inputs for increasing or decreasing rather than relying on special auxiliary relays. Some models also include start and reset inputs.

(3) 2-phase A-B phase type high-speed counter: C251 to C255

These counters support two-phase inputs (C251 to C255) and can handle up to two 32-bit binary up/down counters. They operate in interrupt mode regardless of the scan period. These counters also feature application instructions that allow comparison and output operations independently of logical functions. When a counter is selected, the associated start, reset, and input signals become available. The phase relationship between A and B determines whether the counter counts up or down.

For example, when the A phase signal is ON:

- If B phase goes OFF → ON: Count up

- If B phase goes ON → OFF: Count down