HP 8153A - Page 130

The Condition Registers
You can read a condition register at any time to find the current status of the
node. It is updated continuously. Reading a condition register does not change
its contents.
The Transition Filters
The transition fitters are of two types, a positive transition filter and a negative
transition filter. A 1 in a bit of the transition filter enables that bit.
An enabled bit in a positive transition filter generates a 1 at the output when
the input goes from 0 to 1.
An enabled bit in a negative transition filter generates a 1 at the output when
the input goes from i to 0.
The condition register provides the input to the filters. The output is sent to the
event register.
At power up, all of the bits in both transition registers are set to 0. That is, no
transitions are passed to the event registers.
The Event Registers
The outputs from the transition filters set the bits in the event register. These
bits are only cleared when the register is read, otherwise they stay as they are.
The Enable Registers
The enable register selects which bits affect the next stage of registers. A 1 in a
bit in the enable register, means that the corresponding bit in the event register
is enabled. The enabled bits are ORed together and the result is sent to the
condition register in the next node.
At power up, all of the bits in the enable registers are set to 0,
7-2 Remote Operation • Status Commands