RS-485 multipoint power line modem

• US 5,684,826 A
• Filed: 02/08/1996
• Issued: 11/04/1997
• Est. Priority Date: 02/08/1996
• Status: Expired due to Fees

• Current Assignee: Ace Technology Corporation
• Original Assignee: Ace Technology Corporation
• Inventors: Ratner, Boris
• Primary Examiner(s): Barry, Lance Leonard
• Application Number:
  US08/590,035
• Time in Patent Office: 635 Days
• Field of Search: 340/310.01-310.08, 340/825.06-825.18, 340/870.02-870.03, 375/222-223, 395/200.2
• US Class Current: 375/222
• CPC Class Codes: H04B 2203/5408 using protocols
• CPC Class Codes: H04B 2203/5425 improving S/N by matching impedance, noise reduction, gain control
• CPC Class Codes: H04B 2203/5445 Local network
• CPC Class Codes: H04B 2203/5483 using coupling circuits
• CPC Class Codes: H04B 3/542 the information being in digital form
• CPC Class Codes: H04L 25/45 using electronic distributors

Abstract

A modem enabling multi-point networks to be established over power lines emulating the RS-485 electrical interface standard for data transmissions. The modem includes a data terminal interface unit for exchanging data with a data terminal, a power line interface unit for placing data onto and taking data off of the power line, and a parallel I/O interface connecting the two units and including a network processor implementing a network protocol for sending and receiving messages. The parallel I/O interface provides for very fast data transfers across the parallel I/O interface compared with the rates at which the modem receives data from the power line and from the data terminal. In addition, at least the outgoing data is transferred across the parallel I/O interface in a form intermediate between the serial RS-485 data stream from the data terminal and the message packet that is sent over the power line by the power line interface unit. The parallel I/O interface facilitates reliable and flexible transfers compensating for delays and uncertainties in the transmission rate over the power line.

Claims

1. Apparatus for interfacing a plurality of data terminals over a power line for the exchange of data, said data terminals sending and receiving data according to the RS-485 electrical interface standard, comprising:

a data terminal interface portion for receiving and sending a serial RS-485 data stream from and to a first of said data terminals at a first nominal data rate, said serial RS-485 data stream comprising a plurality of data bytes;

a power line interface portion for receiving data from and sending data to said power line at a second nominal data rate; and

a parallel I/O interface connecting said data terminal interface portion with said power line interface portion for communicating data back and forth therebetween;

wherein said parallel I/O interface comprises;

a network processor implementing a network protocol for sending and receiving messages over said power line through said power line interface portion;

outgoing data transfer means for transferring said plurality of data bytes from said data terminal interface portion to said network processor in an intermediate form at an internal transfer rate substantially greater than said first and second nominal data rates for inclusion in an outgoing message to be passed to said power line interface portion; and

incoming data transfer means for transferring the data in an incoming message received from said power line interface portion to said data terminal interface portion at said internal transfer rate to be passed to said first data terminal as an RS-485 data stream;

whereby said apparatus emulates an RS-485 communications environment for said plurality of data terminals.

2. The apparatus of claim 1 wherein said intermediate form comprises at least one intermediate data packet.

3. The apparatus of claim 1 wherein said outgoing data transfer means and said incoming data transfer means each includes a virtual data buffer having a length in bytes that is variable in response to variations in the speed of communications on the power line.

4. A method of interfacing a plurality of data terminals over a power line for the exchange of data, said data terminals sending and receiving data according to the RS-485 electrical interface standard, comprising the steps of:

providing a network processor implementing a network protocol for sending and receiving messages over said power line, said messages being sent and received over said power line at a first nominal data rate;

receiving a serial RS-485 data stream from a first of said data terminals at a second nominal data rate;

converting said serial RS-485 data stream to a parallel data stream;

feeding said parallel data stream to a first buffer;

forming a first packet from the data in said first buffer as of a prescribed time;

transferring said first packet to a second buffer at a rate substantially greater than said first and second nominal data rates while continuing to feed said parallel data stream to said first buffer;

retrieving said first packet from said second buffer and forming a second packet therefrom, said second packet including data from said first packet and additional network routing data;

transmitting said second packet over said power line according to the protocol of said network processor to at least one other of said data terminals; and

successively repeating said steps of forming a first packet, transferring said first packet, retrieving said first packet and forming said second packet, and transmitting said second packet until all of said serial RS-485 data stream has been transmitted.

5. The method of claim 4 wherein said prescribed time for forming said first packet corresponds to a time when said second buffer is empty.

6. The method of claim 4 wherein said parallel data stream is composed of a plurality of data bytes, and said method further comprises the steps of:

keeping count of the number of bytes in said first buffer; and

forming said first packet from the earliest bytes in said first buffer equal in number to said count at said prescribed time while continuing to feed said parallel data stream to said first buffer.