Touchpoint 4 Serial Communication Protocol Issue 1 09/07
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Communication Port
Access to the Touchpoint4 protocol is through the terminal block on the common
module of Touchpoint4 gas detector controller. This port is designed for bidirectional
communications between the Touchpoint4 instrument and your master.
Signals present at the port conform to RS-485 specifications. The pin-out specifications
are described in the chapter
connectors pin-out
.
Address Setting Procedure
After the networking cabling has been connected to the slave, the slave must be
configured to communicate. Baud rate and address are selectable. Configuration is
performed with the following sequence:
1. Access the menu system and select the
RS485 communication link
settings menu option. Press UP/DOWN, the icon flashes.
2. Press OK, the controller’s current address is displayed.
3. Use UP/DOWN to change the address (between 1 and 16 available).
4. Press OK to accept the change.
The display changes to display the current baud rate.
5. Use UP/DOWN to change the baud rate (1200, 2400, 4800, 9600,
19200 available).
6. Press OK to accept the change.
Please refer to the Technical Manual for more details.
Protocol Specifics
The protocol has been designed for flexibility and efficiency. This byte-wise protocol
communicates information by transferring bytes of data back and forth between master
and slave. A group of bytes for each communication is called a packet.
The master and slave(s) transfer information via data packets. These packets will always
contain bytes to start communication, an address, a length, a command, one or more
data and a checksum.
Additional optional variable-length data bytes or optional parameters can also be sent
or received. This section is a brief overview of the protocol specifics.
Packet Length
Just as all words are not the same length (number of letters), packets may also vary in
length. In this protocol, the length of command and data field is put before command
field in the packet. Your data containing "0x42, 0x41, 0x44" will then become “0x03,
0x42, 0x41, 0x44”.
