Lake Shore 370 User Manual
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Lake Shore Model 370 AC Resistance Bridge User’s Manual6.2.3 Hardware SupportThe Model 370 interface hardware supports the following features. Asynchronous timing is used for the individual bitdata within a character. This timing requires start and stop bits as part of each character so the transmitter and receivercan resynchronized between each character. Half duplex transmission allows the instrument to be either a transmitter or areceiver of data but not at the same time. Communication speeds of 300, 1200, or 9600 Baud are supported. The Baudrate is the only interface parameter that can be changed by the user.Hardware handshaking is not supported by the instrument. Handshaking is often used to guarantee that data messagestrings do not collide and that no data is transmitted before the receiver is ready. In this instrument appropriate softwaretiming substitutes for hardware handshaking. User programs must take full responsibility for flow control and timing asdescribed in Paragraph 6.2.6.6.2.4 Character FormatA character is the smallest piece of information that can be transmitted by the interface. Each character is 10 bits longand contains data bits, bits for character timing and an error detection bit. The instrument uses 7 bits for data in theASCII format. One start bit and one stop bit are necessary to synchronize consecutive characters. Parity is a method oferror 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 delimitersto 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 6-3. Serial Interface SpecificationsConnector Type:Connector Wiring:Voltage Levels:Transmission Distance:Timing Format:Transmission Mode:Baud Rate:Handshake:Character Bits:Parity:Terminators:Command Rate:9-pin D-style connector plugDTEEIA RS-232C Specified50 feet maximumAsynchronousHalf Duplex300, 1200, 9600Software timing1 Start, 7 Data, 1 Parity, 1 StopOddCR(0DH) LF(0AH)20 commands per second maximum6.2.5 Message StringsA message string is a group of characters assembled to perform an interface function. There are three types of messagestrings commands, queries and responses. The computer issues command and query strings through user programs, theinstrument issues responses. Two or more command strings can be chained together in one communication but they mustbe separated by a semi-colon (;). Only one query is permitted per communication but it can be chained to the end of acommand. The total communication string must not exceed 64 characters in length.A command string is issued by the computer and instructs the instrument to perform a function or change a parametersetting. The format is: |
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