HP VXI manual Condition Register Transition Filter Event Register, An Example Sequence

Condition Register

Transition Filter

Event Register

The condition register continuously monitors the hardware and firmware status of the instrument. There is no latching or buffering for this register; it is updated in real time. Condition registers are read-only.0

If there is no command to read a particular condition register, it is simply invisible to you.

The transition filter specifies which types of bit state changes in the condition register will set corresponding bits in the event register. Transition filter bits may be set for positive transitions (PTR), negative transitions (NTR), or both. Positive means a condition bit changes from

0 to 1. Negative means a condition bit changes from 1 to 0. Transition filters are read-write. Transition filters are unaffected by *CLS (clear status) or queries. They are set to instrument-dependent values at power

on and after *RST (reset).

If there are no commands to access a particular transition filter, it has a fixed setting. This setting is specified in the instrument’s programming guide or command dictionary. Most of our VXI instruments assign the transition filter to detect positive transitions only.

The event register latches transition events from the condition register as specified by the transition filter. Bits in the event register are latched, and, once set, they remain set until cleared by a query or *CLS (clear status).

There is no buffering; so while an event bit is set, subsequent events corresponding to that bit are ignored. Event registers are read-only.

Enable Register The enable register specifies which bits in the event register can generate a summary bit. The instrument logically ANDs corresponding bits in the event and enable registers, and ORs all the resulting bits to obtain a summary bit. Summary bits are, in turn, recorded in another register, often the Status Byte. Enable registers are read-write. Enable registers are not affected by *CLS (clear status). Querying enable registers does not affect them. There is always a command to read and write to the enable register of a particular status group.

An Example Sequence

Figure 2-2illustrates the response of a single bit position in a typical status group for various settings. The changing state of the condition in question is shown at the bottom of the figure. A small binary table shows the state of the chosen bit in each status register at the selected times T1-T5.

8 Programming the Status System Chapter 2