Siemens Drum Sequencer

Description
The DRUM function block drives the programmed output bits (OUT1 to OUT16) and the word output (OUT_WORD) with the programmed values (OUT_VAL) of the appropriate step conditioned by the enabling masks (S_MASK) for that step while the DRUM remains on that step. The DRUM advances to the next step when either the event for the step is true and the programmed time for the current step has expired, or the jog input transitions from 0 to 1. When the signal state of input RESET is 1, the DRUM is reset, which sets the current step equal to the preset step (DSP).
The amount of time spent on a step is determined by the product of the DRUM time base preset (DTBP) and the count preset/step values (S_PRESET) corresponding to each step. At the start of a new step, this calculated value is loaded into DCC, which contains the time remaining for the current step. For example, if DTBP equals 2 and the preset value for step 1 equals 100 (100 msec), then DCC equals 200 (200 msec).
A step may be programmed with a time value, or an event, or both. Steps with an event bit that has a signal state of 0 time advance to the next step as soon as the signal state of the event bit is 1. Steps with only a time start timing immediately. Steps with an event bit and a time value greater than 0 begin timing when the signal state of the event bit is 1. The event bits are initialized with a signal state of 1.
When the step pointer is on the last programmed step (LST_STEP) and the time for that step has expired, the signal state of output Q is set to 1; otherwise it is set to 0. Once Q is set, the DRUM remains on that step until reset.
The configurable mask (S_MASK) allows selection of the individual bits in the output word (OUT_WORD) and the output bits (OUT1 to OUT16) that are set/reset by the output values (OUT_VAL). When a bit of the configurable mask has a signal state of 1, the OUT_VAL value sets/resets the corresponding bit. When a bit of the configurable mask has a signal state of 0, the corresponding bit is left unchanged. Each of the bits of the configurable mask for all 16 steps is initialized with a signal state of 1.
The output bit OUT1 corresponds to the least significant bit of the word output (OUT_WORD). The output bit OUT16 corresponds to the most significant bit of the word output (OUT_WORD).

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