Siemens S7-300/400PLC addressing mode - Database & Sql Blog Articles

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Brand AVX TPSE226M035R0125 Low impedance tantalum capacitor AVX 22

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

100V, 250mA, surface mount, high speed switching diode

SMD aluminum electrolytic capacitor

The direct addressing method in Siemens S7-300/400 PLCs is similar to that of the S7-200. However, when it comes to indirect addressing, there are two main types: memory indirect addressing and register indirect addressing. Unlike the S7-200, the S7-300/400 has dedicated pointer registers AR1 and AR2, which make indirect addressing more flexible and powerful. This allows for a wider range of addresses and more convenient operations. 1. Memory Indirect Addressing Compared to the S7-200, the S7-300/400 offers two key differences in memory indirect addressing: - In S7-300/400, you don’t need to create a separate pointer. Instead, you can directly use the “[]” symbol before the address to indicate that it’s an indirect reference. - It supports indirect addressing for binary bit addresses, which is not possible in the S7-200. For example, if you want to read input I22.2 into a local variable LD10, perform an AND operation with I0.0, and output the result to Q0.1, the code would look like this: ``` LP#22.2 TLD10 AI[LD10] A I0.0 = Q0.1 ``` This is equivalent to: ``` AI22.2 A I0.0 = Q0.1 ``` 2. Register Indirect Addressing Register indirect addressing uses the pointer registers AR1 or AR2 to specify an offset. The format is [AR1,m] or [AR2,m], where m represents the offset. The address is determined by combining the value stored in the pointer register with the offset. These registers can store various types of data, including addresses, bytes, and bits, allowing for both internal and cross-area addressing. For instance, you can access memory areas like M (flags), I (inputs), Q (outputs), DBX (data blocks), DIX (data inputs), and L (local variables). The structure of the pointer register includes several fields: - Bit 31: Indicates whether the register contains an address (1) or just data (0). - Bits 24–26: Define the type of address (e.g., I, Q, M, DBX, etc.). - Bits 18–3: Specify the byte address. - Bits 2–0: Specify the bit within the byte. For example, if you want to shift the bit 22.2 into the pointer register and then read from I32.3, the code could be: ``` LP#22.2 LAR1 AI[AR1, P#10.1] A I0.0 = Q0.1 ``` This is equivalent to: ``` AI32.3 A I0.0 = Q0.1 ``` When working with binary bits, remember that each byte corresponds to 8 bits, so offsets should be calculated in octal. Another example involves reading from I21.4 using a pointer register: ``` LP#10.5 LAR1 AI[AR1, P#10.7] A I0.0 = Q0.1 ``` This is equivalent to: ``` AI21.4 A I0.0 = Q0.1 ``` If the pointer register includes an address character, such as M6.0, the code becomes even more efficient: ``` LP#M6.0 LAR1 LIW10 TW[AR1, P#50.0] ``` This is equivalent to: ``` LIW10 TMW56 ``` Using these techniques makes programming on the S7-300/400 much more flexible and powerful compared to older models like the S7-200.