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Lake Shore Model 325 Temperature Controller User’s Manual
Remote Operation 6-3
6.1.3.2 Common Commands
Common Commands are addressed commands that create commonalty between instruments on the bus. All instruments
that comply with the IEEE-488 1987 standard share these commands and their format. Common commands all begin
with an asterisk. They generally relate to “bus” and “instrument” status and identification. Common query commands
end with a question mark (?). Model 325 common commands are detailed in Section 6.3 and summarized in Table 6-9.
6.1.3.3 Device Specific Commands
Device specific commands are addressed commands. The Model 325 supports a variety of device specific commands to
program instruments remotely from a digital computer and to transfer measurements to the computer. Most device
specific commands perform functions also performed from the front panel. Model 325 device specific commands are
detailed in Section 6.3 and summarized in Table 6-9.
6.1.3.4 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 strings or queries can be chained together in one communication but
they must be separated by a semi-colon (;). The total communication string must not exceed 255 characters in length.
A command string is issued by the computer and instructs the instrument to perform a function or change a parameter
setting. When a command is issued, the computer is acting as ‘talker’ and the instrument as ‘listener’. The format is:
<command mnemonic><space><parameter data><terminators>.
Command mnemonics and parameter data necessary for each one is described in Section 6.3. Terminators must be sent
with every message string.
A query string is issued by the computer and instructs the instrument which response to send. Queries are issued similar
to commands with the computer acting as 'talker' and the instrument as 'listener'. The query format is:
<query mnemonic><?><space><parameter data><terminators>.
Query mnemonics are often the same as commands with the addition of a question mark. Parameter data is often
unnecessary when sending queries. Query mnemonics and parameter data if necessary is described in Section 6.3.
Terminators must be sent with every message string. Issuing a query does not initiate a response from the instrument.
A response string is sent by the instrument only when it is addressed as a 'talker' and the computer becomes the 'listener'.
The instrument will respond only to the last query it receives. The response can be a reading value, status report or the
present value of a parameter. Response data formats are listed along with the associated queries in Section 6.3.
6.1.4 Status System
6.1.4.1 Overview
The Model 325 implements a status system compliant to the IEEE 488.2 – 1992 standard. The status system provides a
method of recording and reporting instrument information and is typically used to control the Service Request (SRQ)
interrupt line. A diagram of the status system is shown in Figure 6-1. The status system is made up of register sets, the
Status Byte register, and the Service Request Enable register. Each register set consists of three types of registers,
condition, event, and enable.
6.1.4.1.1 Condition Registers
Each register set (except the Standard Event Register set) includes a condition register as shown in Figure 6-1. The
condition register constantly monitors the instrument status. The data bits are real-time and are not latched or buffered.
The register is read-only.
6.1.4.1.2 Event Registers
Each register set includes an event register as shown in Figure 6-1. Bits in the event register correspond to various
system events and latch when the event occurs. When an event bit is set, subsequent events corresponding to that bit are
ignored. Set bits remain latched until the register is cleared by a query command (such as *ESR?) or a *CLS command.
The register is read-only.