RMS Technologies R325 DRIVER W/PDT - Manual (Page 21)

RMS Technologies Page 21 Version 1.20
R325I Single Axis Controller/Driver Manual 02/13/2006
Apart from the leading ‘#’ being replaced by a ‘*’, the Slaves response to a Command should
be an exact copy of the command message. In the case of a Query the query message is
also echoed but the value or other requested information is added into the reply.
A one character time interval has to be allowed between outgoing and incoming messages,
to allow for line turn-around (Switching between Transmit and Receive). At 57,600 baud, one
character with 11 bits (one start, eight data, and two stop bits) transmits in 191 µS.
4. Validation
Commands are validated by comparing the content of the reply with the content of the
command message on a character by character basis.
Queries are partially validated in a similar manner but the information added by the Slave is
only subjected to credibility tests. When the information returned is deemed critical, repeating
the Query and comparing results can further validate communications.
5. S Message Format
A two-character command/query designator follows the single address character. Depending
on the nature of the command, the command designator may be followed by a numeric ASCII
character string. No separator characters are used, but a carriage return character (0x0D) is
inserted before the termination character in both the outgoing message and the reply.
6. Data Format
Data is transmitted at 57,600 Baud, with eight data bits, no parity, and two stop bits.
7. Recommended Interface Device
The RMS Technologies USB485 Converter Card converts the RS485 connection to a
standard USB connection (1.1 and 2.0 compatible).
8. HyperTerminal Operation
In addition to setting the data format to match that specified in section 6, two settings must be
made in the ASCII setup section. Check ‘Send Line Ends with Line Feeds’ and ‘Echo Typed
Characters Locally’.
When typing by hand line turn-around will occur between characters. This is normally not a
problem, but if you slowly increase the character transmission rate you will find errors
occurring, until you reach a rate where the line is held in the transmit mode for the whole of
the message. Using HyperTerminal’s file transfer system to send messages is not
recommended.
9. Reading Reply Messages
The message read function on the RS232 side of the interface, must make provision for
discarding any characters read that proceed the ‘*’ character. Line turn-around can commonly
generate false characters.
The function should have a time-out associated with waiting for a reply to allow for a non-
operational Slave node. The actual time required is system dependent, but 20mS is a
commonly used value.