West Control Solutions 8700+ - Manual (Page 132)

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59305, Issue 7
– March 2014 ASCII Communications Page 127
14 ASCII Communications
This is simple ASCII protocol provides backwards compatibility with some older products.
ASCII is not available in all models in the range. The Modbus protocol is recommended for
future use.
Refer to the relevant Model Group Section for the ASCII and Modbus Application Layer
(parameter address/ident information).
Physical Layer
The Base address, bit rate and character format are configured via the front panel in
Configuration Mode or by using the PC Configurator software.
Physical layer configuration settings possible are:
Data rate: 1200, 2400, 4800 (default), 9600 and 19,200 bps
Parity: Even
Character format: 7 bits per character. + 1 stop bit.
The transmitter must not start transmission until 3 character times have elapsed since
reception of the last character in a message, and must release the transmission line within 3
character times of the last character in a message.
Note:
Three character times = 1.5ms at 19200, 3ms at 9600, 6ms at 4800, 12ms at 2400 and
24ms at 1200 bps.
Device Addressing
The instrument is assigned a device address by the user using the

parameter in
Configuration Mode. The address may be set to any unique value from 1 (default) to 99. This
address is used to recognise ASCII messages intended for this instrument. The instrument
does not respond to messages that do not match the address that has been assigned to it.
Session Layer
The ASCII protocol assumes half duplex communications. The master device initiates all
communication. The master sends a command or query to the addressed slave instrument
and the slave replies with an acknowledgement of the command or the reply to the query.
Messages from the master device may be one of five types:
Type 1: {S}{N}??*
Type 2: {S}{N}{P}{C}* or R{N}{P}{C}*
Type 3: {S}{N}{P}#{DATA}* or R{N}{P}#{DATA}*
Type 4: {S}{N}{P}I* or R{N}{P}I*
Type 5: {S} {N} \ P S S ? *
All characters are in ASCII code. See the following Parameter Key table for details of the
parameters in brackets { }.