VM Series Displays RS232 User Guide
020-1359-00A
Page | 10
System
6. Communication Control
This defines the feedback command from the monitor to the host controller. When the device
receives a display command from the host controller the command reported to host controller
will be ACK, NAK or NAV.
Note:
There is no reply message when the wrong ID address is used.
6.1 Message Report
Number of Field
Name of Field
Description
Byte 1
Header
Header = 0x21
Byte 2
Monitor ID
Monitor ID
Range: 1 ~ 255
Byte3
Category
0x00
Byte4
Page
0x00
Byte5
MsgLen
Length of message plus Checksum code.
Calculate the length from Control Byte to
Checksum Byte.
Byte6
Control
0x01
Byte7
Data[0]
Copy the received Command code
Byte8~Byte8+(N-1)
Data[1]~Data[N]
Returned data associated with command code
Byte 8+N
Checksum
XOR of all byte in reply/report packet (except
checksum itself)
Example ACK Reply: (Display Address 01)
Header Monitor ID Category Page Length Control Data[0] Data[1]
Checksum
Description
0x21
0x01
0x00
0x00
0x04
0x01
0x00
0x00
0x25
Command is well executed.
Example NAK Reply: (Display Address 01)
Header Monitor ID Category Page Length Control Data[0] Data[1]
Checksum
Description
0x21
0x01
0x00
0x00
0x04
0x01
0x00
0x03
0x26
If the command code is
Data(0), the system will reply
“NAK.”
Example NAV Reply: (Display Address 01)
Header Monitor ID Category Page Length Control Data[0] Data[1] Checksum
Description
0x21
0x01
0x00
0x00 0x04 0x01
0x00
0x04
0x21
Checksum error-
“NAV”.
Command Code Data(1)-
“NAV”.
