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The Status Model Introduction to Programming
Agilent 8163A/B, 8164A/B & 8166A/B Mainframes, Fifth Edition 33
The Status Model
Status Registers
Each node of the status circuitry has three registers:
• A condition register (CONDition), which contains the current status.
This register is updated continuously. It is not changed by having its
contents read.
• The event register (EVENt), which contains details of any positive
transitions in the corresponding condition register, that is, when a bit
changes from 0 → 1. The contents of this register are cleared when it is
read. The contents of any higher-level registers are affected with regard
to the appropriate bit.
• The enable register (ENABle), which enables changes in the event
register to affect the next stage of registers.
The structures of the Operational and Questionable Status Systems are
similar. Figure 4 describe how the Questionable Status Bit (QSB) and the
Operational Status Bit (OSB) of the Status Byte Register are determined.
Figure 3 The Registers and Filters for a Node
The event register is the only kind of register that can affect the next stage
of registers.
NOTE
Enable Registers
To the
Condition Register
of the Next Node
Event Registers
Condition Registers
OR
11111
A positive transition in the condition
causes the corresponding bit of the
to change from 0
→
1.
corresponding event register
register, when a bit changes from 0
→
1,