Sony EVI D70 Technical Manual - Page 32

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-D70/P assigned address 1 from the controller (address 0) is hexadecimal 81H. The packet Command List sent to the EVI-D70/P assigned address 2 is 82H. In the command list, as the header is 8X, input the address of the EVI-D70/P at X. The header of the reply packet from the EVI-D70/P assigned address 1 is 90H. The packet from the EVI-D70/P assigned address 2 is A0H. Some of the commands for setting EVI-D70/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. Header Packet (3 to 16 bytes) Message (1 to 14 bytes) Terminator Byte 1 Byte 2 Byte 3 FF Sender's 1 address 0 Receiver's address Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (MSB) (LSB) 11 11 1111 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (MSB) (LSB) 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. 1 byte Start Stop bit Bit 0 Bit 1 Bit 2 Bit 3 Bit 4 Bit 5 Bit 6 Bit 7 bit. (LSB) (MSB) Fig. 3 Actual waveform for 1 byte. 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 the1V 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. General Commands RxD TxD Command ACK Completion Within 16.7msec(20msec*PAL) Query Commands RxD Within 16.7msec(20msec*PAL) Command Inquiry Pocket TxD 16 Byte 32