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4
VISCA Communication
Specifications
VISCA packet structure
The basic unit of VISCA communication is called a
packet (Fig. 2). 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 BRC-Z330 assigned address 1 from the controller
(address 0) is 81H in hexadecimal. The packet sent to the
BRC-Z330 assigned address 2 is 82H. In the command
list, as the header is 8X, input the address of the BRC-
Z330 to X. The header of the reply packet from the
BRC-Z330 assigned address 1 is 90H. The packet from
the BRC-Z330 assigned address 2 is A0H.
Some of the setting commands for BRC-Z330 can be
sent to all devices at one time (broadcast). In the case of
broadcast, the header should be 88H in hexadecimal.
When the terminator is FFH, it signifies the end of the
packet.
Fig. 2 Packet structure
Note
Fig. 2 shows the packet structure, while Fig. 3 shows the
actual waveform. Data flow will take place with the LSB
first.
Fig. 3 Actual waveform for 1 byte.
Timing Chart
As VISCA command processing can only be carried out
a maximum of one time in a Vertical (V*) cycle, it takes
maximum 4V-cycle time for an ACK/Completion to be
returned.
If the Command and ACK/Completion communication
time is shorter than 1V-cycle time, a command can be
received at every 1V cycle. From this point, if two or
more commands are to be sent successively, wait for a
reply command (an ACK or error message for a general
command, and an inquiry packet for an inquiry
command) of the previous command to be received
before sending the next command.
*1V=16.7 msec (NTSC: 1080/59.94i, 720/59.94P), 20 msec (PAL: 1080/
50i, 720/50P)
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
10
FF
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
11111111
Packet (3 to 16 bytes)
Message (1 to 14 bytes)
Byte 1 Byte 2 Byte 3
Sender’s
address
Receiver’s address
Header Terminator
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
(LSB) (MSB)
Bit 6 Bit 7
1 byte
Start
bit
Stop
bit.
Command
Within 4V
RxD
TxD
ACK Completion
Within 4V
RxD
TxD
Inquiry Packet
Command
General commands
Inquiry commands
16 Bytes