Echelon FT 3150 Smart Transceiver - Manual (Page 83)

FT 3120 / FT 3150 Smart Transceiver Data Book 77
Timer/Counter Input Objects
Pulsecount Input
A timer/counter may be configured to count the number of input edges (up to 65,535) in a fixed time (0.8388608
second) at all allowed input clock rates. Edges may be defined as rising or falling. This object is useful for average
frequency measurements, or tachometer applications. See Figure 3.41.
*If the measurement is new, t
ret
= 52 µs. If a new time is not being returned, t
ret
= 22 µs.
Figure 3.41 Pulse Count Input Latency Values
This is an edge-sensitive function. The clock driving the internal counter in the FT Smart Transceiver is the actual
input signal. The counter is reset automatically every 0.839 second.
The internal counter increments with every occurrence of an active input edge. Every 0.839 second, the content of the
counter is saved and the counter is then reset to 0. This sequence is repeated indefinitely.
The actual active edge of the input depends on whether or not the invert option was used in the declaration of the
function block. The default is the negative edge.
Symbol Description Typ @ 10MHz
t
fin
Function call to input sample 86 µs
t
ret
Return from function 52/22 µs*
0.84 s
STOP START
t
ret
t
fin
READ
TIMER/COUNTER
FLAG AND
EVENT
REGISTER
CLEAR FLAG
END OF
io_in()
START OF
o_in()
mux
Event Register
Event Register
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
System Clock
Divide Chain
Timer/Counter 2
Timer/Counter 1
Reference Figure 3.35
Optional Pull-Up Resistors