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Reference Manual
00809-0100-4696, Rev AA
September 2004
3-13
Rosemount 848L
PS - When the hardware input consists of a continuous train of pulses at a
rate less than 500 PPS, a prescaler can be used to reduce the pulse rate to
something that does not change faster than the equation evaluation rate. The
function is PS (i, divisor) where ‘i’ is the channel number (1-8) and ‘divisor’ is
the number of pulses to count before setting its output true for one equation
evaluation cycle. The counter rolls over at ‘divisor’ and keeps counting. The
user must assure that there is always at least one execution cycle with a false
value from PS for every true value. If the pulse rate exceeds the divisor times
two, then the function returns Bad status and optionally a PlantWeb alert can
be sent. Only ten of these functions are available because they require
storage for previous values.
DO - Channels 9-16 are zero unless set by configured DO or MDO function
blocks. This allows a function block link to set the value from a remote
function block output or HMI screen switch. The values may be referenced in
equations by the DO (d) function. The range of ‘d’ is 1 to 8. To directly drive an
output from an external device the Output Equation would reference DO(d).
NOTE
The value of DO can change during an evaluation cycle if the macrocycle
evaluates the DO block. This may require referencing the DO value in a single
equation to “save” its state.