Chapter 2 Devices, Symbols and Instructions -2,147,483,648 to +2,147,483,647. Besides, four 16-bit registers can be combined into a 64-bit register, i.e. (D+3, D+2, D+1, D) in which the register whose number is smaller represents the lower 16 bits. The highest bit represents either a positive sign or a negative sign, and the values which can be stored in the data registers range from -9,223,372,036,854,776 to +9,223,372,036,854,775,807. The registers can be classified into two types according to their properties: 1. General-purpose register: If the PLC begins to run, or is disconnected, the value in the register will be cleared to zero.
If you want to retain the data when the PLC begins to RUN, you can refer to ISPSoft User Manual for more information. Please notice that the value will still be cleared to zero if the PLC is disconnected. 2. Latched register: If the PLC is disconnected, the data in the latched register will not be cleared. In other words, the value before the disconnection is still retained. If you want to clear the data in the latched area, you can use RST or ZRST. 2_ 2.1.9 Special Data Registers (SR) SR: special data registers. Every special data register has its definition and specific function. The system statuses and the error messages are stored in the special data registers.
Besides, the special data registers can be used to monitor the system statuses. For function descriptions of each special data register (SR), refer to Appendix 2: Special Deta Registers Table 2.1.10 Link Registers (L) The link register is mainly used in for automatic data exchange function. When the data exchange occurs between the AHxxEMC series PLCs, the link register can be used as the buffer. The link registers L0~L65535 have 65536 words and can be used as the common auxiliary registers. 2.1.11 Stepping Relays (S) The function of the stepping relay: The stepping relay can be easily used in the industrial automation to set the procedure.
It is the most basic device in the sequential function chart (SFC). Please refer to ISPSoft User Manual for more information related to sequential function charts. There are 2048 stepping relays, i.e. S0~S2047. Every stepping relay is like an output relay in that it has an output coil, contact A, and contact B. It can be used several times in the program, but it can not directly drive the external load. Besides, the stepping relay can be used as a general auxiliary relay when it is not used in the sequential function chart. 2.1.12 Timers (T) 1. 100 millisecond timer: The timer specified by the instruction TMR takes 100 milliseconds as the timing unit. 2. 1 millisecond timer:
The timer specified by the instruction TMRH takes 1 millisecond as the timing unit. 3. The timers for the subroutine’s exclusive use are T1920~T2047. 4. The accumulative timers are ST0~ST2047. If you want to use the device-monitoring function, you can monitor T0~T2047. 2-7