Grass Valley Switcher Products - Manual (Page 97)

Switcher Products — Protocols Manual 97
Protocol Description
Command Structure
The Peripheral Bus II protocol includes six types of messages: Three are
essential for a fully functional PBus II interface, and three are optional.
• Learn,
• Recall,
• Trigger,
• Query (optional)
• Read (optional), and
• Write (optional).
The peripheral interface command set has been constructed from ASCII
characters. This permits the commands to be displayed on a conventional
computer terminal. Additionally, the ASCII characters used for command
codes are different from those used for data in order to simplify the con-
trolled device software and help prevent coding errors.
Each message sent out on the peripheral bus has a three part format. A
unique ASCII character serving as a keyword is sent first, additional data
follows, and finally a carriage return terminates the message. In order to
eliminate problems caused by interleaving spaces and line feeds that may
have been inserted for readability, those characters are ignored in message
parsing by both the controlling and controlled devices.
Twenty-three ASCII characters comprise the complete set of characters
available. Seven ASCII characters represent keywords, and 16 characters
represent data (
Table 104 ).
Table 104. Peripheral Bus II ASCII Characters
Category Character Hex Description
Keyword
L 4C Learn
R 52 Recall
T 54 Trigger
Q 51 Query
S 53 Read
W 57 Write and Read Response
0D End or Message
Data
1-9 30-39
A-F 41-46