Omega Model CYD211 User’s Manual
Remote Operation
4-3
4.1.3 Character
Format
A character is the smallest piece of information that can be transmitted by
the interface. Each character is 10 bits long and contains data bits, bits for
character timing and an error detection bit. The instrument uses 7 bits for
data in the ASCII format. One start bit and one stop bit are necessary to
synchronize consecutive characters. Parity is a method of error detection.
One parity bit configured for odd parity is included in each character.
ASCII letter and number characters are used most often as character data.
Punctuation characters are used as delimiters to separate different
commands or pieces of data. Two special ASCII characters, carriage return
(CR 0DH) and line feed (LF 0AH), are used to indicate the end of a
message string.
Table 4-1. Serial Interface Specifications
Connector Type: 9-pin D-style plug
Connector Wiring: DTE
Voltage Levels: EIA RS-232C Specified
Transmission Distance: 50 feet maximum
Timing Format: Asynchronous
Transmission Mode: Half Duplex
Baud Rate: 9600
Handshake: Software timing
Character Bits: 1 Start, 7 Data, 1 Parity, 1 Stop
Parity: Odd
Terminators: CR(0DH) LF(0AH)
Command Rate: 20 commands per second maximum
4.1.4 Message
Strings
A message string is a group of characters assembled to perform an interface
function. There are three types of message strings commands, queries and
responses. The computer issues command and query strings through user
programs, the instrument issues responses. Two or more command or query
strings can be chained together in one communication but they must be
separated by a semi-colon (;). The total communication string must not
exceed 64 characters in length.
