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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-300/P assigned address 1 from the

controller (address 0) is hexadecimal 81H. The packet

Header

Sender's

address

Bit 7

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

(MSB)

Note

Fig. 2 shows the packet structure, while Fig. 3 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

Receiver's address

(LSB)

Fig. 2 Packet structure

Start

Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5

bit

(LSB)

Fig. 3 Actual waveform for 1 byte.

sent to the BRC-300/P assigned address 2 is 82H. In

the command list, as the header is 8X, input the

address of the BRC-300/P at X. The header of the

reply packet from the BRC-300/P assigned address 1 is

90H. The packet from the BRC-300/P assigned

address 2 is A0H.

Some of the commands for setting BRC-300/P 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.

Byte 3

Bit 7

Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

(MSB)

1 byte

Bit 6 Bit 7

General Commands

Command

RxD

TxD

Within16.7msec(20msec*PAL)

Query Commands

Command

RxD

TxD

Terminator

Stop

bit.

(MSB)

ACK Completion

16.7msec(20msec*PAL)

(LSB)

Inquiry Pocket

16 Byte