Corrections to INTERBUS specifications as listed in the Understanding Device Level Busses publication.
INTERBUS (formerly INTERBUS-S)
INTERBUS a serial shift register bus which forms a ring-tree topology. INTERBUS is a high efficiency, deterministic protocol that operates in full duplex transfer mode and can transfer up to 256 words (4096 inputs and 4096 outputs) of data per network. The protocol is token-less and all modules have equal and full priority. INTERBUS contains a built in protocol known as PCP (Peripheral Communications Protocol). PCP allows the sending of large data blocks to intelligent devices, without effecting cyclic data update time of the INTERBUS network. There can be up to 62 PCP devices on a single INTERBUS network. The 500kbits/s baud rate allows the use of less expensive cabling. INTERBUS is divided into remote and local bus segments, however there is no protocol change. Branching and bus terminal modules allow the user to route cable to suit the plant layout. All data flows serially through every module. There can be 512 INTERBUS devices (nodes), with 254 allowed on the main remote bus. There can be up to 63 devices on a local bus segment. There can be up to 400 meters between nodes, and a total INTERBUS distance of 12.8km. INTERBUS masters directly map I/O data into a memory area of the host PC/PLC. There are also additional channels available for commands and messages to the master.
Bus Type: Full duplex segmented serial shift register.
Total Number of Nodes: 512, of which 254 may be on the main remote bus. Local bus segments may contain up to 63 devices.
Bus Topology: Ring - Tree. All data is circulated through each device. Every module is a repeater.
Distance: 400m between drops, with a total network length of up to 12.8 km.
Transmission media: Shielded two twisted pair plus ground for RS-485 remote bus segments. Fiber-Optic, Infrared, Slip Ring, and Slotted Wave-Guide mediums are also supported. ST Local bus consists of 5 wire TTL level signals.
Input words per node(device): 2 bits to 32 words.
Output words per node(device): 2 bits to 32 words.
Protocol Speed: 500 kbits/s
Bus Power: Nodes can be individually powered, or powered via Installation Remote Bus of up to 4.5 amps at 50 meters.
Duplicate Address Detection: By default, physical positioning determines the modules address. It is not possible to have duplicate addresses, and no address (dip-switch) settings are required for devices. The applications has the option of logically addressing the network to leave spaces for future expansion.
Attendance check per scan: The master performs an ID cycle during each startup. The host then knows every device present , and the length of the network. Should this change for any reason during operation, the master will automatically determine the cause and location of the error. Local bus devices can be switched in and out of the ring by the host, without stopping the data transfer (Hot Swapping).
Error Detection: Full CRC by all devices on both outgoing and return data paths. This function is built into the protocol chip.
Error Correction: Data is held locally in each device until CRC checking has been performed. Should an error be detected the data is discarded. Only after successful CRC checking, is the data latched to the outputs. The master automatically records the top-ten exact locations of CRC errors and provides this information to the host for evaluation during normal bus operation. The host can determine how many sequential CRC errors can occur before stopping the network.
Address setting: Not applicable, see Duplicate Address Detection.
Node Parameter Programming: INTERBUS has a built in block transfer protocol called PCP (peripheral-communication-protocol). PCP co-exists with Process Data(I/O data) on the same network. PCP allows the parameterization of and communication to intelligent devices without hindering network performance. There can be up to 62 PCP devices per network.
Correction to Chapter 5 Table on page 28:
Media Access Method
Token-less Serial Shift Ring. Branching tree topology.
Collision Avoidance/Detection
No collisions possible
Messages (When do nodes talk)
Every nodes talks during every scan. All nodes have full/equal priority. Network is full duplex allowing inputs to be read as outputs are written.
Comments
Master Slave system. Master performs all protocol controls and diagnostics.
Corrections to Published Material
