Drum Instruction
Programming
6–9
Drum Instruction Programming
S Counts/Step – The number of timer counts the drum spends in each
step. Each step has its own counts parameter. However, programming
the counts/step is optional.
S Timer Value – the current value of the counts/step timer.
S Counter # – The counter number specifies the first of four consecutive
counters which the drum uses for step control. You can monitor these to
determine the drum’s progress through its control cycle. The DL05 has
128 counters (CT0 – CT177 in octal).
S Events – Either an X, Y, C, S, T, or CT type discrete point serves as
step transition inputs. Each step has its own event. However,
programming the event is optional.
WARNING: The outputs of a drum are enabled any time the CPU is in Run Mode.
The Start Input does not have to be on, and the Reset input does not disable the
outputs. Upon entering Run Mode, drum outputs automatically turn on or off
according to the pattern of the current step of the drum. This initial step number
depends on the counter memory configuration: non-retentive versus retentive.
The choice of the starting step on powerup and program-to-run mode transitions are
important to consider for your application. Please refer to the following chart. If the
counter memory is configured as non-retentive, the drum is initialized the same way
on every powerup or program-to-run mode transition. However, if the counter
memory is configured to be retentive, the drum will stay in its previous state.
Counter Num-
Function
Initialization on Powerup
ber
Non-Retentive Case Retentive Case
CT(n) Current Step
Count
Initialize = 0 Use Previous (no
change)
CT(n + 1) Counter Timer
Value
Initialize = 0 Use Previous (no
change)
CT(n + 2) Preset Step Initialize = Preset Step # Use Previous (no
change)
CT(n + 3) Current Step # Initialize = Preset Step # Use Previous (no
change)
Applications with relatively fast drum cycle times typically will need to be reset on
powerup, using the non-retentive option. Applications with relatively long drum cycle
times may need to resume at the previous point where operations stopped, using the
retentive case. The default option is the retentive case. This means that if you
initialize scratchpad V-memory, the memory will be retentive.
Powerup State of
Drum Registers
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