Echelon FT 3150 Smart Transceiver - Manual (Page 85)

FT 3120 / FT 3150 Smart Transceiver Data Book 79
Timer/Counter Input Objects
A call to this function returns the current value of the quadrature count since the last read operation. The counter is
then reset and ready for the next series of input transitions. The count returned is a 16-bit signed binary number,
capped at ±16K.
The number shown in the diagram above is the minimum time allowed between consecutive transitions at either input
of the quadrature function block. For more information, see the, Neuron Chip Quadrature Input Function Interface
engineering bulletin.
Totalcount Input
A timer/counter may be configured to count either rising or falling input edges, but not both. Reading the value of a
totalcount object gives the number of transitions since the last time it was read (0 to 65,535). Maximum frequency of
the input is one-quarter of the input clock rate, for example 2.5MHz at a maximum of 10MHz FT Smart Transceiver
input clock. This object is useful for counting external events such as contact closures, where it is important to keep
an accurate running total. See Figure 3.43.
Figure 3.43 Totalcount Input Latency Values
Symbol Description Typ @ 10MHz
t
fin
Function call to input sample 92 µs
t
ret
Return from function 61 µs
read input_value = 4, reset read, reset
t
ret
t
fin
READ
TIMER/
COUNTER
FLAG AND
EVENT REGISTER
CLEAR FLAG
END OF
io_in()
START OF
io_in()
Event Register
Event Register
Timer/Counter 1
Timer/Counter 2
mux
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
Reference Figure 3.35
Optional Pull-Up Resistors