ABB TPU2000 Technical Manual page 269

Where D1 Lo is the low nibble of the first data byte and D1 Hi is the high nibble of the first data byte, D2 Lo is the low
nibble of the second data byte and D2 Hi is the high nibble of the second data byte, and D3 Lo is the low nibble of the third
data byte and D3 Hi is the high nibble of the third data byte.
The checksum is 256 minus the sum of the ASCII characters in bytes 1 to 8. CS Lo is the low byte and CS Hi is the high
byte of the checksum.
Example (3 data bytes, ascii characters 4, 8, and 7)
STX
C/D
D1 Lo
D1 Hi
D2 Lo
D2 Hi
D3 Lo
D3 Hi
CS Lo
CS Hi
The three data bytes translate to:
Checksum = 256 - (STX + C/D + D1L + D1H + D2L + D2H + D3L + D3H)
256 - (2 + 0 + 4 + 3 + 8 + 3 + 7 + 3) = E2
Transmission and reception convention
To acknowledge successful receipt of a message, an ACK is transmitted. The three byte message packet is 0x000013. For an
unsuccessful reception, ie. a checksum error or an error in command processing, a NACK is transmitted. The three byte
message packet is 0x100013.
The commands for the TPU2000 relay can be catagorized into three basic types according to the response that is expected by
the master. When a command or data is received, the TPU2000 must acknowledge if the reception was successful.
1-Simple Commands: A simple command directs the TPU2000 to perform specific actions. After the successful completion
of these actions, the TPU2000 transmits an ACK as seen below.
2-Upload Data This type of command requests the TPU2000 to transmit specific data. The proper transmission of this data
is the TPU2000 acknowledge of this type of command as seen below.
TPU2000/2000R Modbus/Modbus Plus Automation Guide
= hex 2 --> Start of transmission
= hex 0 --> Data type of message
= hex 4 --> Data 1 low byte
= hex 3 --> Data 1 high byte
= hex 8 --> Data 2 low byte
= hex 3 --> Data 2 high byte
= hex 7 --> Data 3 low byte
= hex 3 --> Data 3 high byte
= hex 2 --> Checksum low byte
= hex E --> Checksum high byte
Data 1 = 34 --> ascii 4
Data 2 = 38 --> ascii 8
Data 3 = 37 --> ascii 7
Master
Figure 7 - Simple Command Communication Flow
Command
ACK
DPU2000
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