Grass Valley Switcher Products - Manual (Page 42)

42 Switcher Products — Protocols Manual
Section 2 — Editor Protocol
Editor Protocol Access
This Editor protocol is based upon, but not identical to, the proposed
SMPTE (Society of Motion Picture and Television Engineers) Digital
Control Interface, which establishes a means for the orderly flow of data
over a serial bus.
The major components of the protocol are shown in Figure 2 and discussed
in the following paragraphs.
Figure 2. Components of the Editor Interface Protocol
Break Character
The main component of the Editor protocol is a 1-1/2 character-length
“break.” A break consists of a spacing or logical low (0) condition on the
serial bus (see Figure 2-2) followed by a minimum of two bit-times of
marking (logic 1) condition. The Bus Controller (editor) transmits a break
to the switcher, forewarning of an impending message (
Figure 3 ).
Figure 3. Break Character
The break forces all tributaries, or listeners (such as the switcher’s editor
port), from the “Idle” state into the “Active” state. A break can be sent only
by the Edit Controller. When the switcher receives the break, it ceases all
bus communications, resets any communication error condition, and pre-
pares to receive an address (
Figure 4 ).
Break
Character
Address
Byte
Command/Message Blocks
0350-06
1 Bit Time (26 S @ 38.4K Baud)
Spacing Data, 17 to 20 Bit Times
SMPTE Break Character
Marking Data, 2 or More Bit Times
First Character of
Address Byte
8063_02_02_r0