Emerson manual Rosemount 848L, Reference Manual, 00809-0100-4696,Rev AA September

Rosemount 848L

Reference Manual

00809-0100-4696, Rev AA September 2004

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.

Direction	Reset	Shift 1	Shift 2	Shift 3
Left	00000000	00000001	00000010	00000100
Right	00000000	10000000	01000000	00100000

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.

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