Siemens SIMATIC S7-200 System Manual page 149

Multiple-Segment Pipelining of PTO Pulses
In multiple-segment pipelining, the S7-200 automatically reads the characteristics of each pulse
train segment from a profile table located in V memory. The SM locations used in this mode are
the control byte, the status byte, and the starting V memory offset of the profile table (SMW168 or
SMW178). The time base can be either microseconds or milliseconds, but the selection applies to
all cycle time values in the profile table, and cannot be changed while the profile is running.
Execution on the PLS instruction starts multiple segment operation.
Each segment entry is 8 bytes in length, and is composed of a 16-bit cycle time value, a 16-bit
cycle time delta value, and a 32-bit pulse count value. Table 6-34 shows the format of the profile
table. You can increase or decrease the cycle time automatically by programming a specified
amount for each pulse. A positive value in the cycle time delta field increases cycle time, a
negative value in the cycle time delta field decreases cycle time, and 0 results in an unchanging
cycle time.
While the PTO profile is operating, the number of the currently active segment is available in
SMB166 (or SMB176).
Table 6-34 Profile Table Format for Multiple-Segment PTO Operation
Byte Offset Segment
0
#1
1
3
5
#2
9
11
13
(Continues) #3
1 Entering a value of 0 for the number of segments generates a non-fatal error. No PTO output is generated.
Pulse Width Modulation (PWM)
PWM provides a fixed cycle time output with a
variable duty cycle. (See Figure 6-29.) You can
specify the cycle time and the pulse width in either
microsecond or millisecond increments:
Cycle time: y
- -
Pulse width time:
-
As shown in Table 6-35, setting the pulse width equal to the cycle time (which makes the duty
cycle 100 percent) turns the output on continuously. Setting the pulse width to 0 (which makes the
duty cycle 0 percent) turns the output off.
Table 6-35 Pulse Width Time and Cycle Time and Reactions in the PWM Function
Pulse Width Time/ Cycle Time
Pulse width time >= Cycle time value
Pulse width time = 0
Cycle time < 2 time units
Description of Table Entries
Number of segments: 1 to 255
Initial cycle time (2 to 65,535 units of the time base)
Cycle time delta per pulse (signed value) (- -32,768 to 32,767 units of the time
base)
Pulse count (1 to 4,294,967,295)
Initial cycle time (2 to 65,535 units of the time base)
Cycle time delta per pulse (signed value) (- -32,768 to 32,767 units of the time
base)
Pulse count (1 to 4,294,967,295)
(Continues)
10 µs to 65,535 µs or
µ µ
2 ms to 65,535 ms 2 t 65 535
0 µs to 65,535 µs or
0 ms to 65,535 ms
Reaction
The duty cycle is 100%: the output is turned on continuously.
The duty cycle is 0%: the output is turned off.
The cycle time defaults to two time units.
S7-200 Instruction Set
1
Cycle Time
Pulse Width
Time
Figure 6-29 Pulse Width Modulation (PWM)
Chapter 6
Pulse Width
Time
135