User guide

Chapter 3 - Input/Output Interfaces
82 FT 3120 / FT 3150 Smart Transceiver Data Book
to drive an audio transducer, or to drive a frequency to voltage converter to generate an analog output. See
Figure 3.45.
Frequency Resolution and
Maximum Range at 10MHz
Figure 3.45 Frequency Output Latency Values
A new frequency output value will not take effect until the end of the current cycle. There are two exceptions to this
rule. If the output is disabled, the new (non-zero) output will start immediately after
t
fout
. Also, for a new output value
of zero, the output is disabled immediately and not at the end of the current cycle.
A disabled output is a logic zero by default unless the invert keyword is used in the I/O object declaration. The
resolution and range for this object scale with FT Smart Transceiver input clock rate, for example: resolution
from 0.1 to 12.8 µs and range from 6.55 to 839 ms at 40MHz.
Symbol Description Typ @ 10MHz
t
fout
Function call to output update 96 µs
t
ret
Return from function 13 µs
System Clock
Divide Chain
Timer/Counter 1
Timer/Counter 2
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
High Current Sink Drivers
END
OF io_out()
t
ret
NEW OUTPUT
APPEARS ON PIN
HARDWARE
UPDATED
INTERNALLY
t
fout
START
OF io_out()
TIME
FREQUENCY
OUTPUT
ONE CYCLE
CLK Resolution Range Unit
0 0.4 26.21 µs
1 0.8 52.42 µs
2 1.6 104.86 µs
3 3.2 209.71 µs
4 6.4 419.42 µs
5 12.8 838.85 µs
6 25.6 1677 µs
7 51.2 3355 µs