1 Basic Principles of PLC Ladder Diagram DVP-PLC Application Manual 1-5 Device Functions Internal relay The internal relay does not have connection with the external. It is an auxiliary relay inside the PLC with the functions same as those of the auxiliary (middle) relay in the electric control circuit. Every internal relay corresponds to a basic internal storage unit and can be driven by the contacts of the input relay, contacts of the output relay and the contacts of other internal devices. There are no limitations on the times of using the contacts of the internal relay and there will be no output from the internal relay, but from the output point. Device indication:
M0, M1, …, M4095 are indicated as M and numbered in decimal form. Step DVP series PLC offers a step-type control program input method. STL instruction controls the transfer of step S, which makes it easy for the writing of the control program. If you do not use any step program in the control program, step S can be used as an internal relay M as well as an alarm point. Device indication: S0, S1, …S1023 are indicated as S and numbered in decimal form. Timer The timer is used for timing and has coil, contact and register in it. When the coil is On and the estimated time is reached, its contact will be enabled (contact A closed, contact B open). Every timer has its fixed timing period (unit:
1ms/10ms/100ms). Once the coil is Off, the contact iwlwl be disabled (contact A open, contact B closed) and the present value on the timer will become “0”. Device indication: T0, T1, …, T255 are indicated as T and numbered in decimal form. Different No. refers to different timing period. Counter The counter is used for counting. Before using the counter, you have to give the counter a set value (i.e. the number of pulses for counting). There are coil, contact and registers in the counter. When the coil goes from Off to On, the counter will regard it as an input of 1 pulse and the present value on the counter will plus “1”. We offer 16-bit and 32-bit high-speed counters for our users.
Device indication: C0, C1, …, C255 are indicated as C and numbered in decimal form. Data register Data processing and value operations always occur when the PLC conducts all kinds of sequential control, timing and counting. The data register is used for storing the values or all kinds of parameters. Every register is able to store a word (16-bit binary value). Double words will occupy 2 adjacent data registers. Device indication: D0, D1, …, D11999 are indicated as D and numbered in decimal form. File register The file register is used for storing the data or all kinds of parameters when the data registers required for processing the data and value operations are insufficient.
Every file register is able to store a 16-bit word. Double words will occupy 2 adjacent file registers. In SA/SX/SC series MPU, there are 1,600 file registers. In EH2/SV/EH3/SV2 series MPU, there are 10,000 file registers. There is not an actual device No. for a file register. The reading and writing of file registers should be executed by instructions API 148 MEMR, API 149 MEMW, or through the peripheral device HPP02 and WPLSoft. Device indication: K0 ~ K9,999, numbered in decimal form.