Appendix B: Master-Slave Protocol
VT400 Technical Manual, Rev. A5 70 Doc # UM-VT400-EN
? Command: Upload Status
This is the main command used to poll the slave or slaves. The slave replies with the
current weight being measured, or with a message if bit 0 of the status byte is ‘1’.
Master
Transmission
ID SLAVE ? XXXXXX BCS
XXXXXX: These bytes are not used; fill with Space character (20h).
For RS485, Master Transmission contains only ID Slave, ? and BCS.
Slave Response
ID SLAVE Weight Status Weight Digits BCS
Weight Status Byte: see table below.
Weight Digits: 6 bytes (ASCII), including decimal point. Most
significant byte first.
Example For sending the ? (3F hex) command for RS485:
Address 66 (66 decimal=B ascii=42 hex ), the message is “B?BCS”.
BCS is calculated as 42 XOR 3F = 7D = 1111101, the 6 LSB of the 7D are 111101, add 00 to the 2
MSB and it becomes 00111101= 3D (“=” hex).
The message to send from the PC will be “B?=”.
Weight Status Byte:
B7 B6 B5 B4 B3 B2 B1 B0
0 1 1 In weight
range/out of
range
0=IN,
1=OUT
Sign
0= +
1= -
No motion
0=NO,
1=YES
Error Status
0=NO,
1=YES
Mode
0=Gross,
1=Net
0 Command: Reset Slave
Resets the slave to its power-on condition.
Master
Transmission
ID SLAVE 0 XXXXXX BCS
XXXXXX: These bytes are not used; fill with Space character (20h).
Slave Response None
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