Echelon FT 3150 Smart Transceiver - Manual (Page 81)

FT 3120 / FT 3150 Smart Transceiver Data Book 75
Timer/Counter Input Objects
*If the measurement is new, t
ret
= 52 µs. If a new time is not being returned, t
ret
= 22 µs.
Figure 3.39 Ontime Latency Values
This is a level-sensitive function. The active level of the input signal gates the clock driving the internal counter in the
FT Smart Transceiver.
The actual active level of the input depends on whether or not the invert option was used in the declaration of the
function block. The default is the high level.
Period Input
A timer/counter may be configured to measure the period from one rising or falling edge to the next corresponding
edge on the input. Table 3.6 shows the resolution and maximum time measured for various clock selections. This
object is useful for instantaneous frequency or tachometer applications. Analog-to-digital conversion can be
implemented using a voltage-to-frequency converter with this object. See Figure 3.40.
Symbol Description Typ @ 10MHz
t
fin
Function call to input sample 86 µs
t
ret
Return from function 52/22 µs*
mux
Event Register
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
System Clock
Divide Chain
Optional Pull-Up Resistors
Reference Figure 3.35
Event Register
Timer/Counter 2
Timer/Counter 1