Echelon FT 3150 Smart Transceiver - Manual (Page 75)

FT 3120 / FT 3150 Smart Transceiver Data Book 69
Serial I/O Objects
The Touch I/O object can run at FT Smart Transceiver clock rates of 5MHz and 10MHz only. This is because the
Touch I/O object is designed to meet the Touch Memory timing specification at those FT Smart Transceiver clock
speeds only. The Touch I/O object is not supported at clock rates faster than 10MHz or slower than 5MHz.
For more specific information on the mechanical, electrical, and protocol specifications, refer to the Book of DS19xx
Touch Memory Standards, available from Dallas Semiconductor Corporation.
Wiegand Input
This input object provides an easy interface to any card reader supporting the Wiegand standard. Data from the reader
is presented to the FT Smart Transceiver through the use of two of its first eight I/O pins, IO0 – IO7. Up to four
Wiegand devices may be connected to the FT Smart Transceiver. Data is read MSB first.
Wiegand data starts as a negative-going pulse on one of the two pins selected. One input represents a logical 0 bit and
the other pin a logical 1, as selected through the I/O declaration. The bit data on the two lines are mutually exclusive
and are spaced at least 150 µs apart. Figure 3.34 shows the timing relationship of the two data lines with respect
to each other and the FT Smart Transceiver.
Any unused I/O pin from IO0 to IO7 may be optionally selected as the timeout pin. When the timeout pin goes high,
the function aborts and returns. The watchdog timer of the application processor is automatically updated during the
operation of this input object.
Incoming data on any of the Wiegand input pins is sampled by the FT Smart Transceiver every 200ns at a 10MHz
clock (scales inversely with the clock frequency). Since the Wiegand data is usually asynchronous, care must be
taken in the application program to ensure that this function is called in a timely manner in order that no incoming
data is lost.