Parameterising 1xcounter/16xdigital input module
Measuring the frequency (mode 3)
12
Parameter setting
12.6
12.6.6
l
12.6-11
EDSPM-TXXX-3.0-04/2004
12.6.6 Measuring the frequency (mode 3)
In mode 3, the counter operates as a frequency meter. For this purpose the counter
counts the number of rising edges of signal A of a specified time slot.
The time slot can be determined by selecting a starting value (Data In) and a
reference frequency (Ref. Freq.) in the Rx PDO.
Byte Assignment
5 Reference frequency
00
h
16 MHz
01
h
8MHz
02
h
4MHz
03
h
1MHz
04
h
100 kHz
05
h
10 kHz
06
h
1kHz
07
h
100 Hz
08
h...
FF
h
not permissible
T
w
Time slot
T
=
1
⋅ n
f
ref
Reference frequency (is transmitted in byte 5)
ref
n Starting value (is transmitted in bytes 0 ... 3)
When bit 2 (Load) changes from LOW to HIGH in byte 4 (Control), the counter is
pre-assigned with the starting value from byte 0 to 3 (Data In).
The software gate which releases the counting process, is opened, when bit 0
(Start) in the byte 4 (Control)has HIGH level. It is closed as soon as bit 1 (Stop)has
HIGH level.
When the software gate is open:
z
The reference counter is started by the first rising edge of signal A (E.0) and
then incremented with every rising edge of the reference clock.
z
When the reference counter reaches the starting value (time T
w
has elapsed),
the current count value is shifted into the Tx PDO in byte 0 ... 3 (Data Out).
z
Then, the counter and reference counter are automatically reset and the next
frequency measurement starts with the next rising edge of signal A.
z
If two rising edges do not occur in the signal A within the time slot T
w
,the
count value for this measurement is interpreted with zero.
The counter can be cleared at any time via a HIGH level in byte 4 (Control), bit 3
(Clear). The loaded value remains valid unti a new value is loaded.
Reference frequency
Time slot calculation
Load signal
Start/ stop signal
Asignal
Clear signal
To Next Page
Loading...
Need help?
General
