Lakeshore Learning Materials 622 - Manual (Page 87)

Lake Shore Model 620/622/623/647 Magnet Power Supply User’s Manual
Mainframe Control Bus Operation B-3
B6.0 CONTROL BUS SERIAL INTERFACE OPERATION
The host computer initiates the serial interface link and transmits either a command or a query to the
Mainframe. The Mainframe stores the characters in a buffer until the carriage return (CR), line feed (LF)
terminator sequence. After receiving the terminators, the Mainframe responds appropriately to a query, if
present, and stores the new input parameters.
Queries output requested data immediately following the processing of the command and terminator
sequence. If more than one query is sent, the last query received is acknowledged. Commands and queries
can be sent in the same command string. For example, the command string ISET+10 VSET+10 updates the
current setting to +10 amps and the voltage setting to +10 volts. No query was sent, therefore the Mainframe
returns no response. The command string ISET+10 VSET+10 ISET? causes the Mainframe to return the current
setting as well.
The serial interface shares device specific commands with the IEEE-488 interface. Tables B-1 and B-2
summarize the commands. See Chapter 3 of this manual for detailed command descriptions. The END and
TERM remote commands are IEEE-488 interface specific commands not supported by the serial interface.
When programming a Mainframe from the serial interface, consider the notes below. See Chapter 3 for
additional notes on commands.
• The control bus serial interface transmission mode (asynchronous half duplex), format (10 bits per
character; 1 start, 7 data, 1 odd parity, and 1 stop), and baud rate (9600) are all fixed at the factory as
outlined previously in the Serial Interface Specifications.
• The control bus cannot be used for remote interfacing if a Multiple Mainframe (MMF) configuration is used.
In MMF mode, the Control Bus is used for Mainframe to Mainframe communications.
• End of string terminators are fixed at (CR)(LF).
• A query must be added to the end of a command string if the Mainframe is required to return information.
• Chain commands together with a semi-colon, a comma, or a blank. Some programming languages do not
allow separators other than a blank.
• At 9600 baud, each character takes about 1 millisecond to transmit. Some host computers DMA serial
interface access. The program must allow for the transmission time delay before looking for a query
response.
• Characters received by the Mainframe are stored in a buffer. After receiving the terminators, the Mainframe
stores any new parameters and responds to the query (if requested). The Mainframe requires about
100 milliseconds to store new parameters before receiving any more new commands.
• The Mainframe implements new parameters and updates measurement data once per 500 millisecond
operation cycle. Do not send new parameters or request data at a rate faster than 2 Hz.