Echelon FT 3150 Smart Transceiver - Manual (Page 72)

Chapter 3 - Input/Output Interfaces
66 FT 3120 / FT 3150 Smart Transceiver Data Book
The chip select logic for the Neurowire slave can be handled by the user through a separate bit input object, along
with an appropriate handshaking algorithm implemented by the user application program. In order to prevent
unnecessary timeouts, the setup and hold times of the chip select line, relative to the start and end of the external
clock, must be satisfied.
The timeout input pin can either be connected to an external timer or to an output pin of the FT Smart Transceiver that
is declared as a oneshot object.
Serial Input/Output
Pin IO8 may be configured as an asynchronous serial input line, and pin IO10 may be configured as an asynchronous
serial output line. The bit rates for input and for output may be independently specified to be 600, 1200, 2400, or
4800 bits/second at a 10MHz input clock rate. The data rate scales proportionally to the input clock rate. For example,
at 40MHz, the bit rates would be 2400, 4800, 9600, or 19,200 bits/second.
The frame format is fixed at 1 start bit, 8 data bits, and 1 stop bit; and up to 255 bytes may be transferred at a time.
Either a serial input or a serial output operation (but not both) may be in effect at any one time. The interface is half-
duplex only. This function suspends application processing until the operation is completed. On input, the io_in()
request will time out after 20 character times if no start bit is received. If the stop bit has the wrong polarity (it
should be a 1), the input operation is terminated with an error. The application code can use bit I/O pins for
flow control handshaking if required. This function is useful for transferring data to serial devices such as
terminals, modems, and computer serial interfaces. See Figures 3.31 and 3.32.
Figure 3.31 Serial Input Object
Symbol Description Typ @ 10MHz
t
fin
Function call to input sample
Min (first sample)
Max (timeout) 67 µs
20 byte frame
t
ret
Return from function 10 µs
END OF
FRAME
DATA
ONE FRAME
START BIT
APPEARS
START OF
io_in()
t
fin
8 7 6 5 4 3 2 1
TIME
SERIAL
INPUT
ST
A
R
T
ST
A
R
T
ST
OP
END OF
io_in()
t
ret
Serial Output
Serial Input
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7