Filter
Top Products
Reference Manual
00809-0100-4696, Rev AA
September 2004
Rosemount 848L
3-18
TP (power, target) - Whenever power transitions from false to true, the value
of the internal timer is set to the target and the value of the function is true.
The value of the function will become false after the target amount of time has
elapsed. This function is similar to TOF except that a timing cycle is only
initiated by the rise of power. Power may go false or stay true without affecting
the timing cycle. The cycle is restarted anytime that power goes true after the
function has had at least one evaluation cycle as false.
Latching Functions
A latch is a two state device that can be set to true or reset to false. It will
retain its state when both commands are false. It will not retain its state
through a device restart. The initial state is Reset. Two latch functions are
required to define the behavior when both commands are true, depending on
which state should be dominant. The result of the function is the state of the
latch.
SR (set, reset) - The parameters set and reset are functions. If both are true
then set wins and the result of the function is true.
RS (set, reset) - The parameters set and reset are functions. If both are true
then reset wins and the result of the function is false.
Shifting Functions
A shift register is a set of bits that moves each bit to the next bit position when
the command to shift is given. The vacant bit is filled with the value of the
input. The 848L shift functions contain 8 bit registers. The bit parameter
selects the bit in the register to test. The value of the function is the value of
the tested bit. The shift may be to the left or the right. The following table
shows the state of the register for three shifts after the register has been
reset. The input is true during the first shift evaluation and false thereafter.
The right most bit is bit 1 and the left most bit is bit 8.
The reset parameter clears the register, overriding both input and shift. Reset
is an optional parameter, but the function can be written with three parameters
or four. Do not use an extra comma if reset is omitted.
The register data will be cleared on a processor restart (i.e. power cycle).
SHL (input, shift, reset, testbit) - The parameters input, shift, and reset are
functions. The parameter testbit is a constant that is constrained to be in the
range of 1 to 8. The reset function is optional. If reset is present and true, the
8 bit register is cleared to zero and the result of the function is false.
Otherwise, if shift is true then bit 7 will be moved to bit 8, bit 6 to bit 7, bit 5 to
bit 6, bit 4 to bit 5, bit 3 to bit 4, bit 2 to bit 3, bit 1 to bit 2, and the value of input
will become the value of bit 1. Then the bit specified by testbit will be tested to
determine the value of the function.
Direction Reset Shift 1 Shift 2 Shift 3
Left 00000000 00000001 00000010 00000100
Right 00000000 10000000 01000000 00100000