92
c
HAPTER
6:
Computer Interface Operation
Model 335 Temperature Controller
6.2.4 Status System
Overview
The Model 335 implements a status system compliant to the IEEE-488.2 standard.
The status system provides a method of recording and reporting instrument informa-
tion and is typically used to control the Service Request (SRQ) interrupt line. A dia-
gram of the status system is shown in FIGURE 6-1. The status system is made up of
status 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.
6.2.4.1 Condition Registers
Each register set (except the Standard Event Register set) includes a condition regis-
ter as shown in FIGURE 6-1. The condition register constantly monitors the instru-
ment status. The data bits are real-time and are not latched or buffered. The register
is read-only.
6.2.4.2 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.
6.2.4.3 Enable Registers
Each register set includes an enable register as shown in FIGURE 6-1. An enable regis-
ter determines which bits in the corresponding event register will set the summary
bit for the register set in the Status Byte. The user may write to or read from an enable
register. Each event register bit is logically ANDed to the corresponding enable bit of
the enable register. When an enable register bit is set by the user, and the correspond-
ing bit is set in the event register, the output (summary) of the register will be set,
which in turn sets the summary bit of the Status Byte register.
