Eurotherm Drives 590 DRV Digital, Product Manual, Page: 221 / 318

590 DRV Digital DC Drive Product Manual App. H - 13
Appendix H RS422 Communications (Ports P1 & P2)
H
Termination
The computer uses the termination procedure when it wishes to stop selecting one 590 Digital drive and establish
connection with another. This is achieved by sending the ‘establish connection’ sequence. The computer retains
master status and transmits an (EOT) character to reset all instruments on the data link to be responsive to the next
GID-UID address parameter.
BINARY COMMUNICATIONS
This mode is similar to the ASCII mode. This section concentrates on presenting parts that are different from the
ASCII mode.
Specifications
Character Format
Each byte is transmitted as 11 bits rather than the 10-bit format used by the ASCII mode. This is because a control bit
is used to indicate control characters or data characters. The format is represented by the following:
1 Start bit (LOW)
7 Data bits (LSB first)
1 Control bit
1 Even parity bit
1 Stop bit (HIGH)
Note: The control bit is 0 for control characters and 1 for data characters.
The Message
Messages received from the supervisor can be in any of several modes. They can be divided into two categories; the
first is “main messages” and the second is “continuation messages.” Before presenting the format of these messages,
the following defines the symbols used in the messages. These symbols are divided into two parts, control characters
and data characters.
Control Characters
(EOT) Indicates the end of transmission. The master sends it at the start of a new message to clear the line.
(STX) Start of text character.
(ENQ) Inquiry character. The master sends it as the last character of any type of a polling message.
(ETX) End of text character. It is followed by another character containing the checksum.
(ETB) End of block character. The 590 Digital drive sends it instead of the (ETX) when it wishes to reply to a
multi parameter inquiry. The (ETB) indicates the end of a block, but not the end of a message. Each
block contains information on up to eight parameters. The (ETB) is used in replies to inquiry polling
and multiparameter polling (these are explained below).
(ACK) Positive acknowledgment character.
(NAK) Negative acknowledgment character.