Echelon FT 3150 Smart Transceiver - Manual (Page 50)

Chapter 3 - Input/Output Interfaces
44 FT 3120 / FT 3150 Smart Transceiver Data Book
Nibble Input/Output
Groups of four consecutive pins between IO0 – IO7 may be configured as nibble-wide input or output ports, which
may be read or written to using integers in the range 0 to 15. This is useful for driving devices that require BCD data,
or other data four bits at a time. For example, a 4x4 key switch matrix may be scanned by using one nibble to
generate an output (row select — one of four rows), and one nibble to read the input from the columns of the switch
matrix. See Figures 3.12, 3.13, and 3.14.
The direction of nibble ports may be changed between input and output dynamically under application control (see
the Neuron C Programmer’s Guide). The LSB of the input data is determined by the object declaration and can be any
of the IO0 – IO4 pins.
Figure 3.13 Nibble Input Latency Values
Symbol Description Typ @ 10MHz
t
fin
Function call to sample
IO0 – IO4 41 µs
t
ret
Return from function
IO0
IO1
IO2
IO3
IO4 18 µs
22.8 µs
27.5 µs
32.3 µs
37 µs
Figure 3.12 Nibble I/O
High Current Sink Drivers
Optional Pull-Up Resistors
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
t
ret
t
fin
TIME
INPUT PIN
SAMPLED
END OF
io_in()
START OF
io_in()
INPUT