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VISCA Communication
Specifications
VISCA packet structure
The basic unit of VISCA communication is called a
packet (Fig.1). The first byte of the packet is called the
header and comprises the sender's and receiver's
addresses. For example, the header of the packet sent
to the FCB-H11 assigned address 1 from the controller
(address 0) is hexadecimal 81H. The packet sent to the
FCB-H11 assigned address 2 is 82H. In the command
Header
Sender's
address
1
Bit 7
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(MSB)
Note
Fig. 1 shows the packet structure, while Fig. 2 shows
the actual waveform. Data flow will take place with
the LSB first.
Timing Chart
As VISCA Command processing can only be carried
out one time in a Vertical cycle, it takes the maximum
1V cycle time for an ACK/Completion to be returned.
If the Command/ACK/Completion communication
time can be cut shorter than the 1V cycle time, then
every 1V cycle can receive a Command.
From this point, if 2 or more commands in a row are to
be sent, wait for the first command (for normal
commands, an ACK or an error message, for query
commands, an Inquiry Packet) to be carried out before
sending the next one.
Packet (3 to 16 bytes)
Message (1 to 14 bytes)
Byte 1
Byte 2
Byte 3
0
Receiver's address
(LSB)
Fig. 1 Packet structure
Start
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
bit
(LSB)
Fig. 2 Actual waveform for 1 byte.
list, as the header is 8X, input the address of the
FCB-H11 at X. The header of the reply packet from
the FCB-H11 assigned address 1 is 90H. The packet
from the FCB-H11 assigned address 2 is A0H.
Some of the commands for setting FCB-H11 units can
be sent to all devices at one time (broadcast). In the
case of broadcast, the header should be hexadecimal
88H. When the terminator is FFH, it signifies the end
of the packet.
1
1
1
1
Bit 7
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(MSB)
1 byte
Stop
Bit 6 Bit 7
bit.
(MSB)
General Commands
Command
Query Commands
Command
Command List
Terminator
FF
1
1
1
1
(LSB)
ACK Completion
More than 16.7 msec
(20msec 50Hz system)
More than 16.7 msec
(20msec 50Hz system)
Inquiry Packet
16 Byte
19
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