Echelon FT 3150 Smart Transceiver - Manual (Page 39)

FT 3120 / FT 3150 Smart Transceiver Data Book 33
Hardware Considerations
Hardware Considerations
Tables 3.1 through 3.5 list the 34 different I/O objects available. Various I/O objects of different types may be used
simultaneously. Figure 3.3 summarizes the pin configuration for each of the I/O objects. For the electrical
characteristics of these pins, refer to the FT 3120 and FT 3150 Smart Transceiver Datasheet. The following sections
contain detailed descriptions of all the I/O objects. The application program may optionally specify the initial values
of digital outputs. Pins configured as outputs may also be read as inputs, returning the value last written. Pins IO4 –
IO7 have optional pull-up current sources that act like pull-up resistors (see Figure 3.1). These are enabled with a
Neuron C compiler directive (#pragma enable_io_pullups). Pins IO0 – IO3 have high sink capability. The others have
standard sink capability. Pins IO0 – IO7 have low-level detect latches. The latency and timing values described
later in this section are typical at 10MHz. The accuracy of these values is ± 10%. Most latency values scale down
at higher input clock rates and scale up at lower input clock rates.
The I/O pull-ups are always enabled during the stack initialization and BIST task. This can cause a problem in some
applications, for example driving a relay. The best solution is to use an I/O that does not have a pull-up. However, if
an I/O with a pull-up must be used, a pull-down resistor could be used to overcome the effects of the pull-up.
Typically, a pull-down in the range of 2.4k to 2.7k is adequate.
Ω Ω