Allen Bradley PLC-5 Classic Controller Complete Guide

The battery uses 1770-XY (AA size lithium thionyl chloride, Tadiran TL5104）。 At 60 ° C and 100% power outage time, the average lifespan is about 329 days; Up to 2 years at 25 ° C. If the system is powered off for a long time and memory needs to be maintained, it is recommended to regularly replace the battery or use EEPROM to store programs.

2.4 Complementary I/O Configuration

Complementary I/O is a unique feature of PLC-5/15 and/25: it assigns the I/O group address of one rack to another physical rack, and the modules in both racks perform opposite functions (input and output pairing). For example, the input module of the main rack corresponds to the output module of the complementary rack, and both use the same input/output mapping table. This configuration can be used to increase the number of I/O points (up to double) or achieve status display, but it is not recommended for redundant control.

When configuring complementary I/O, it is necessary to follow:

Cannot pair input module with input module (they will compete for the same input image bit)

The output module can be paired with the output module (simultaneously controlling actuators and indicators)

The local rack of the processor does not support complementary I/O

The combination of 32 point module and 1 slot addressing, 16 point module and 2 slot addressing cannot use complementary I/O

Detailed explanation and selection strategy of addressing mode

The classic PLC-5 processor supports three addressing modes, each of which determines the relationship between the slots in the I/O rack and the I/O mapping table.

3.1 2-Slot Addressing

Each I/O group corresponds to two physical slots, and each group is assigned a 16 bit input word and a 16 bit output word. Suitable for 8-point modules, but cannot use 32-bit modules. If using 16 point modules, they must be installed in pairs (input modules in even slots, output modules in odd slots), otherwise a slot must be left vacant. The 8-point module can be mixed and placed arbitrarily.

3.2 1-Slot Addressing

Each physical slot corresponds to an I/O group (one word input, one word output). You can mix 8-point and 16 point modules freely. The 32 point module must be installed in pairs in adjacent even/odd slots (slot 0 and slot 1). If not paired, one of the slots must be vacant.

3.3 Half Slot Addressing (1/2-Slot Addressing)

Each physical slot corresponds to two I/O groups (two word inputs, two word outputs), and each 32 point module occupies one word. The 8-point and 16 point modules can also be used, but it will result in a higher waste of I/O points. This mode does not support forced access to the high-order words corresponding to empty slots or low-density modules.

3.4 Rack Number Allocation Rules

Regardless of the addressing mode, an I/O rack is always composed of 8 I/O groups. The relationship between rack and chassis size is shown in the following table:

Number of chassis slots: 2 slots for addressing, 1 slot for addressing, half slot for addressing

4 slots, 1/4 rack, 1/2 rack, 1 rack

8 slots 1/2 rack 1 rack 2 racks

12 slots 3/4 racks 1.5 racks 3 racks

16 slots, 1 rack, 2 racks, 4 racks

The default rack number for the local rack of the processor is 0, which can be changed to 1 through bit 2 of the processor status word S: 26. The remote I/O rack number cannot conflict with the extended local rack number. For example, if an 8-slot expansion local rack is configured as group 0-3 of rack 2, the remote I/O rack cannot be configured as group 4-7 of rack 2.

Communication system configuration

The classic PLC-5 processor supports two main networks: DH+(Data Highway Plus) and remote I/O.

4.1 DH+Network

DH+uses token passing protocol with a transmission rate of 57.6kbps and can connect up to 64 sites. Each site can send a maximum of 271 bytes of data during the token holding period. DH+links can use daisy chain or trunk/branch topology. The maximum length of mainline cables is 3048 meters (10000 feet), and the maximum length of branch lines is 30.5 meters (100 feet).

Performance influencing factors:

Number of nodes: Each non message node occupies approximately 1.5ms of token holding time, while message nodes occupy up to 38ms

Message size and quantity: Messages exceeding the single packet limit (271 bytes) require multiple token polling

Target node location: Response time is affected by the token passing order (see manual figure 5.3 and 5.4 for comparison)

Internal processing load of the processor

If programming is required on the DH+network, it is recommended to set up a dedicated programming DH+link separately to avoid affecting the real-time performance of the process control network. In addition, do not add or remove nodes online or perform online programming during production operation, as it may cause token loss and network reconstruction (which may take several seconds).

4.2 Remote I/O Link

The remote I/O link uses Belden 9463 dual axis cable (1770-CD), supporting 57.6kbps (up to 3048 meters), 115.2kbps (1524 meters), and 230.4kbps (762 meters). All devices must use the same baud rate.

Scanner mode vs. adapter mode:

Scanner mode: PLC-5/15 or/25 serves as a remote I/O master station, scanning I/O data in remote racks and updating it synchronously with local I/O. Each remote I/O rack transmits one data block per scanning cycle.