Publication 1763-RM001C-EN-P - October 2009
476
System Status File
Free Running Clock
This register contains a free running counter. This word is cleared (0)
upon entering an executing mode.
Bits in status word 4 can be monitored by the user program. The bits turn
on and off at a particular rate (cycle time). The On/Off times are identical,
and are added together to determine the cycle time.
S:4 Free Running Clock Comparison for SLC 500 and MicroLogix Controllers
The Free Running Clocks in the SLC 500 and MicroLogix controllers
function the same, but have different resolutions. The resolution of the
Free Running Clock depends upon which controller you are using.
•
SLC 500 and MicroLogix 1000: 10 ms/bit (0.010 seconds/bit)
•
MicroLogix 1100, MicroLogix 1200 and MicroLogix 1500: 100 µs/bit
(0.0001 seconds/bit)
The following table illustrates the differences.
Address
Data Format
Range
Type
User Program Access
S:4
binary
0 to FFFF
status
read/write
Free Running Clock Cycle Times (all Times are in Seconds)
Bit
SLC 500 and MicroLogix 1000
MicroLogix 1100, MicroLogix 1200 and
MicroLogix 1500
On/Off Time
Cycle Time
On/Off Time
Cycle Time
S:4/0
0.010
0.020
0.0001
0.0002
S:4/1
0.020
0.040
0.0002
0.0004
S:4/2
0.040
0.080
0.0004
0.0008
S:4/3
0.080
0.160
0.0008
0.0160
S:4/4
0.160
0.320
0.0016
0.0320
S:4/5
0.320
0.640
0.0032
0.0640
S:4/6
0.640
1.280
0.0064
0.1280
S:4/7
1.280
2.560
0.0128
0.2560
S:4/8
2.560
5.120
0.0256
0.5120
S:4/9
5.120
10.240
0.0512
0.1024
S:4/10
10.240
20.480
0.1024
0.2048
S:4/11
20.480
40.960
0.2048
0.4096
S:4/12
40.960
81.92
0.4096
0.8192
S:4/13
81.92
163.84
0.8192
1.6384
S:4/14
163.84
327.68
1.6384
3.2768
S:4/15
327.68
655.36
3.2768
6.5536
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