Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Reexamination Certificate
1998-10-19
2001-05-08
Lee, Thomas (Department: 2182)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
C340S870030, C340S870030
Reexamination Certificate
active
06230224
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an RS-485 interface, and more particularly, to a circuit for connecting one master node to a large number of slave nodes in a communication network management system.
2. Description of the Related Art
An RS-485 interface is a 2-wire differential drive transmission system. When a supervisory control system of a communication network (or transmission network) is designed using an RS-485 interface, a multidrop connection circuit having a master node and slave nodes is widely used. In communication between the master node and the slave nodes, there is used a polling technique by the master node using a unique identification (ID) number. In an earlier RS-485 multidrop connection circuit, the number (fan-out) of slave nodes which can be connected to one RS-485 common line is 32. The master node sequentially transmits/receives request and response data with the 32 slave nodes.
The master node and the slave nodes transmit/receive data by setting an enable signal to a logic “HIGH (1)” or logic “LOW (0)”. One master node is connected to 32 slave nodes at a maximum through an RS-485 common line. The master node has a driver and a receiver. Each of the slave nodes also has a receiver and a driver. The communication between the master node and the slave nodes is done on the basis of the master node. In more detail, the master node sets an enable signal to a logic “LOW” level and transmits data by using an ID number of a slave node which it is to communicate with. If the data has been transmitted, the master node sets the enable signal to a logic “HIGH” level to maintain its drive at a high impedance state. The respective slave nodes receive the data from the master node. A slave node receiving request data corresponding to its own ID number sets its enable signal to a logic “LOW” level and transmits response data to the master node. If the response data has been transmitted, the corresponding slave node sets its enable signal to a logic “HIGH” level to maintain its drive at a high impedance state. Thus the master node sequentially communicates with all of the slave nodes.
However, since the earlier RS-485 multidrop connection circuit has a maximum of 32 slave nodes connected to one RS-485 common line, it is impossible to construct a supervisory control network consisting of hundreds or thousands of nodes. Therefore, it is necessary to expand the fan-out.
The following patents each discloses features in common with the present invention: U.S. Pat. No. 5,305,215 to Brekkestran et al., entitled Expandable, Mobile, Modular Microcomputer System For AN Off-Road Vehicle, U.S. Pat. No. 4,882,702 to Struger et al., entitled Programmable Controller With I/O Expansion Module Located In One Of I/O Module Positions For Communication With Outside I/O Modules, U.S. Pat. No. 5,060,134 to Hunninghaus, entitled Action Direction Port Expansion Circuit And System, U.S. Pat. No. 5,014,236 to Pogorzelski et al., entitled Input/Output Bus Expansion Interface, U.S. Pat. No. 5,802,327 to Hawley et al., entitled Device For SCSI Expansion, U.S. Pat. No. 5,805,833 to Verdun, entitled Method And Apparatus For Replicating Peripheral Device Ports IN AN Expansion Unit, U.S. Pat. No. 5,603,051 to Ezzet, entitled Input/Output Processor With A Local Memory providing Shared Resources For A Plurality Of Input/Output Interfaces On AN I/O Bus, U.S. Pat. No. 5,684,966 to Gafford et al., entitled Method For Operating A Repeater For Distributed Arbitration Digital Data Buses, U.S. Pat. No. 4,947,386 to Preschutti, entitled Fixed Gain Fixed Loss Amplification System, U.S. Pat. No. 5,455,700 to Thompson et al., entitled Regenerative Communication Channel Extender, and U.S. Pat. No. 5,673,258 to Helbig et al., entitled Method And Apparatus For The Enlargement Of The Reach Of The Transmission Channel Between Functional Groups Of ANISDN-User Interface.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a fan-out expansion circuit for a 1:N (hundreds or thousands of nodes) multidrop connection between a master node and slave nodes in designing a centralized communication network management system using RS-485.
To achieve the above and other objects of the present invention, there is provided a fan-out expansion circuit including a master node, a plurality of line control units, and a plurality of slave nodes. The master node communicates with the respective slave nodes by a polling technique using an identification number of the slave node. The line control units control the transmitting/receiving direction of data upon communication between the master node and the slave nodes. Each of the line control units has one side connected to the master node via a first RS-485 common line and has another side connected to each of the slave nodes via a second RS-485 common line. A maximum of 32 line control units can be connected to the master node. A maximum of 32 slave nodes can be connected to each of the line control units.
REFERENCES:
patent: 4882702 (1989-11-01), Struger et al.
patent: 4947386 (1990-08-01), Preschutti
patent: 5014236 (1991-05-01), Pogorzelski et al.
patent: 5060134 (1991-10-01), Hunninghaus
patent: 5305215 (1994-04-01), Brekkestran et al.
patent: 5390038 (1995-02-01), Cecchini
patent: 5408228 (1995-04-01), Wnendt et al.
patent: 5455700 (1995-10-01), Thompson et al.
patent: 5603051 (1997-02-01), Ezzet
patent: 5673258 (1997-09-01), Helbig et al.
patent: 5684966 (1997-11-01), Gafford et al.
patent: 5710755 (1998-01-01), Chen
patent: 5802327 (1998-09-01), Hawley et al.
patent: 5805833 (1998-09-01), Verdun
patent: 5875310 (1999-02-01), Buckland et al.
patent: 5996038 (1999-11-01), Looi et al.
patent: 6070214 (2000-05-01), Ahern
MEV Limited.;Isolated RS485 Repeater: Instruction Manual(1994);wysiwyg://91http://www.mev-ltd.demon.co.uk/repman.htm.
The DIFAR44 RS485 Repeaterand schematic diagrams; by R.E. Smith; www.rs485.com/pdifar44.html.
Quick Reference For RS485, RS 422, and RS232 and RS423; by Ron Smith; www.rs485.com/rs485spec.html.
Quatech;QTM-8520R RS-485 to RS-232 Converter Module with RS-485 Site Isolation; www.quatech.com/shopquatech/products/prod4243.asp.
Quatech;QTM-8510 RS-485 Isolated Repeater Module; www.quatech.com/shopquatech/prod...d533.asp!shop=off&placard=2000101111755.
Paper by Jan Stanek discussing the RS-422 and RS-485 in comparison with RS-232; www.hw.cz/english/docs/rs485/rs485.html.
RPT-RS485 Physical Repeater RS485 Technical Description; by SysMik GmbH Dresden; www.sysmik.de/data_htm/e_repeater_rs485.html.
RS-422/485 Repeaters RA-48; www.westermo.se/products/ra-48.html.
Adam-4510/4510S/4520/4522; General/Isolated RS-422.485 Repeater Isolated/General RS-232 to 422/485 Converter; www.advantech.com.
Bushnell , Esq. Robert E.
Elamin Abdelmoniem
Lee Thomas
Samsung Electronics Co,. Ltd.
LandOfFree
Fan-out expansion circuit for RS-485 multidrop connection does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fan-out expansion circuit for RS-485 multidrop connection, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fan-out expansion circuit for RS-485 multidrop connection will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2561420