Bit Sequencer - GE PACSystems RX7i Cpu Programmer's Reference Manual

Chapter 4. Ladder Diagram (LD) Programming
4.2.3

Bit Sequencer

The Bit Sequencer (BIT_SEQ) function performs a bit sequence shift through a series of contiguous
bits.
The operation of BIT_SEQ depends on the value of the reset input (R), and both the
current value and previous value of the enabling power flow input (EN):
R Current EN Previous
Execution Execution
ON ON/OFF
OFF OFF
ON
The reset input (R) overrides the enabling power flow (EN) and always resets the sequencer. When R
is active, the current step number is set to the value of the optional N operand. If you did not specify
N, the step number is set to 1. All bits in the bit sequencer, ST, are set to 0, except for the bit pointed
to by the current step, which is set to 1.
When EN is active and R is not active, and the previous EN was OFF, the bit pointed to by the current
step number is cleared. The current step number is incremented or decremented, based on the
direction (DIR) operand. Then the bit pointed to by the new step number is set to 1.
When the step number is being incremented and it goes outside the range of
■
(1  step number  Length), it is set back to 1.
When the step number is being decremented and it goes outside the range of
■
(1  step number  Length), it is set to Length.
The parameter ST is optional. If it is not used, BIT_SEQ operates as described above, except that no
bits are set or cleared. The function just cycles the current step number through its allowed range.
BIT_SEQ passes power to the right whenever it receives power.
Note: Before using the BIT_SEQUENCER function block, the current step number (Word 1 in the
control block) must be set to an integer value between 1 and the length, as defined in the
function block properties. Failure to properly initialize the step number in the
BIT_SEQUENCER function block may result in the CPU going to STOP-HALT mode.
Asserting the Reset parameter (R), before using the BIT SEQUENCER function block assures
that the current step number is set to a valid value.
70 PACSystems* RX7i, RX3i and RSTi-EP CPU Programmer's Reference Manual
EN Current Bit Sequencer Execution
Execution
ON/OFF Bit sequencer resets
Bit sequencer increments/decrements by
ON
1
OFF Bit sequencer does not execute
ON/OFF Bit sequencer does not execute
GFK-2950C