Vaddio Sony EVI-HD1 PTZ Camera - Manual (Page 20)

20
Command List
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 EVI-HD1 assigned address 1 from the controller
(address 0) is hexadecimal 81H. The packet sent to the
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.
Fig. 2 Packet structure
Packet (3 to 16 bytes)
Message (1 to 14 bytes) Header Terminator
Byte 1 Byte 2 Byte 3
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.
Start
bit Stop
bit.
1 byte
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
1 0
FF
Bit 7
(MSB)
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
(LSB)
1 1 1 1 1 1 1 1
Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5
(LSB) (MSB)
Bit 6 Bit 7
Query Commands
General Commands
16 Byte
Command
ACK Completion
More than 16.7 msec
(20msec 50Hz system)
Inquiry Packet
More than 16.7 msec
(20msec 50Hz system)
Command
Sender’s
address
Receiver’s address