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AMASS Data Embedded Control Network (ECN) Protocol Specifications

Physical

The Embedded Control Network ( ECN ) is configured as an RS-485 or modem-based multi-drop environment supporting up to 32 modules over a distance of 4000 feet on single or dual twisted pair cable. The network operates at 9.6 or 19.2 Kbaud rates with the ability to increase these rates up to 115.2 Kbaud. An additional pair is also specified for the routing of 24 Volt or Volt DC power. An important feature of the AMASSER ECxxx line of products is that most modules provide 2500 Vrms isolation between the network and the I/O functions being provided.

Protocol

The Embedded Control Network (ECN) protocol is configured as a master-slave environment supporting a simple & reliable multi-node ASCII based command - response message system. Message strings begin with an address byte followed by the message body, followed by a carriage return byte and terminated with an 8 bit binary checksum. The protocol allows broadcast messages, module identification, and individual module firmware reset ability.

Command Messages

In order to communicate with the AMASSER ECN device, the host controller sends a message to the device. The first byte of the message string is an "address" byte, which consists of an ASCII character which represents the module's node address. In order to support up to 32 remote nodes on a network, the addressing scheme ranges from ASCII "0" (30H) to ASCII "9" (39H), then from ASCII "A" (41H) to ASCII "V" (56H). Following the node address byte is a one or two byte command which allow various I/O operations to be initiated. The network commands available to the host machine for the ECN device are listed below. Further commands are listed in the manual of that particular device.

Following the command byte is the body of the message which contains the parameters required for the execution of the command (if applicable). Following the body of the message is a carriage return byte (0dH) followed by a one-byte checksum which is the one's complement of the sum of all the bytes in the message including the carriage return byte, but not including the one-byte checkum.

The second last character of the message is always "CR" (0DH). This "CR" character must never be used anywhere else in the message string and must always be followed by the 8-bit checksum.  The host controller must turn off its transmitter and enable its receiver within 10 millisec after sending the checksum in half duplex operation mode.

Response Messages

The AMASSER ECN module responds to the host computer by sending a response message to the host computer. The first byte of the response message string is an "address" byte, which consists of an ASCII character which represents the AMASSER ECN device's node address. The addressing scheme ranges from ASCII "0" (30H) to ASCII "9" (39H), then from ASCII "A" (41H) to ASCII "V" (56H) and is set by the Change Node Address Command (see below) and is stored in the on-board EEPROM located on the ECN device. Following the address byte is the body of the response message which contains the parameters ( if any ) requested by the host computer. Following the body of the message is the carriage return and one-byte checksum which is the one's complement of the sum of all the bytes in the message including the carriage return byte, but not including the one-byte checksum.

The second last character of the message is always "CR" (0DH). This "CR" character must never be used any where else in the message string and must always be followed by the 8-bit checksum.  The slave must transmit its response at least 10 millisec after receiving the checksum from the host in half duplex operation mode.
 

Message Length

-- A string of bytes or characters will be at least four bytes in length and not more than 36 bytes in length.

Response Message Timeout

The response message must be received within 100 millisec from the time the last byte (checksum byte) of the command message was transmitted.

Byte Frame Format

-- All transmissions will be asynchronous having 1 start bit, 8 data bits, no parity and 1 stop bit.

Baud Rate

-- 19,200 or 9600 - Software Selectable

ECN Network Commands:

As a minimum, all ECN-based products shall support the following commands.  All other commands shall be hardware-specific but conform to the guidelines set forth in this protocol.
  1. Change Node Address Command A
    • command: aAb<cr><cksum> where b = new node address
    • response: b<cr><cksum>
  2. Send ECN Identification String I
    • command: aI<cr><cksum>
    • response: a<identification string><cr><cksum>
  3. Send acknowledgment !
    • command: a!<cr><cksum>
    • response: a<cr><cksum>
  4. Reset The Module # (if applicable)
    • command: a#<cr><cksum>
    • response: none Wait 10 milliseconds, then send Acknowledgment
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