Touchpoint 4 Serial Communication Protocol Issue 1 09/07
Time diagram
Figure 1. Communication time diagram
Protocol Packet Definition
Packet Format
The format of packets using Touchpoint4 SERIAL COMMUNICATION PROTOCOL is as
follows:
Figure 2. Protocol packet format
Start Code
Size: 1 byte. Always 0x7F.
Slave Address
Size: 1 byte.
Represents the Touchpoint4 gas detector controller address,
0X01 to 0X10 (1 to 16 decimal).
Length
Size: 1 byte.
The number of bytes in the Command field and Data field.
The total packet length is 4 bytes larger than this.
Command
Size: 1 byte.
This is 0x30, 0x40 or 0x41 as defined in the remainder of this book.
Data
Size: 0-250 byte(s).
This section varies according to the chosen command and may
be omitted.
Checksum
Size: 1 byte
The bit-wise XOR result of all the previous bytes in the packet.
This makes the XOR of the entire packet 0X00.
Start
Code
Slave
Address
Length
Command
Data
Checksum
5
