Grass Valley Switcher Products - Manual (Page 44)

44 Switcher Products — Protocols Manual
Section 2 — Editor Protocol
Address Byte
Once the break has been received, the Editor protocol advances to the
active state and begins expecting a one-byte address. The switcher will
respond to the switcher address 30H (Hexadecimal), when transmitted by
the Edit controller. After receiving the address, the Editor protocol accepts
command/message block transmissions containing commands, data
requests, and other data directed toward the switcher. As long as commu-
nication errors do not occur, the Editor protocol can skip the break/address
sequence during the remainder of the transmissions. Command/message
blocks can be sent repeatedly, one after another, without break interrup-
tions.
The address is one byte long and directed to a specific tributary. If the
received address matches the tributary’s assigned address, the tributary
advances to the Selected state and awaits instructions. The address of the
switcher is fixed as 30H. In response to the address, the 3000 transmits an
acknowledgment byte of 84H to the controller, indicating the change in
status to the “Selected” State. If an address of 31H is received, the switcher
transmits an acknowledgment byte of 84H to the controller, but stays in the
“Active” State. If the address does not match, the tributary drops off the bus
(goes Idle) and awaits another break.
Command/Message Block Structure
In the Selected state, the Editor protocol receives command/message
blocks that direct switcher operations. The basic message structure is
shown in
Figure 5 .
Figure 5. Message Structure
The maximum length of a message is 255 bytes plus the byte count byte. At
a baud rate of 38,400, the maximum length command/message takes more
than 4 fields to complete.
The Editor protocol can handle data continuously, receiving a contiguous
stream of command/message blocks. Such an ability enables multiple
switcher operations to be performed without constant cycling through the
Message Bytes
Effects
Addr. Byte
Command
Code Byte Byte Count
Byte
Maximum Size
255 Bytes
0350-09