Echelon FT 3150 Smart Transceiver - Manual (Page 38)

Chapter 3 - Input/Output Interfaces
32 FT 3120 / FT 3150 Smart Transceiver Data Book
Overview
The FT 3120 and FT 3150 Smart Transceivers connect to application-specific external hardware via 11 pins, named
IO0-IO10. These pins may be configured in numerous ways to provide flexible input and output functions with
minimal external circuitry. The programming model (Neuron C language) allows the programmer to declare one or
more pins as I/O objects. An I/O object provides programmable access to an I/O driver for a specified on-chip I/O
hardware configuration and a specified input or output waveform definition. The program can then refer to these
objects in io_in and io_out() system calls to perform the actual input/output function during execution of the program.
Certain events are associated with changes in input values. The task scheduler can thus execute associated application
code when these changes occur.
There are 34 different I/O objects available for use with the FT Smart Transceivers. Most I/O Objects are available in
the FT Smart Transceiver system images by default. If an object not included in the default system image is required
by an application, the development tool will link the appropriate objects into available memory space. For FT 3120
Smart Transceiver designs, this means that internal EEPROM space must be used for the additional object. For FT
3150 Smart Transceiver designs, the object will be added to an external flash or ROM region beyond the 16KB space
reserved for the system image.
The FT Smart Transceivers have two 16-bit timer/counters on-chip (see Figure 2.7). The input to timer/counter 1,
also called the multiplexed timer/counter, is selectable among pins IO4 – IO7, via a programmable multiplexer (mux)
and its output may be connected to pin IO0. The input to timer/counter 2, also called the dedicated timer/counter, may
be connected to pin IO4 and its output to pin IO1. The timer/counters are implemented as a 16-bit load register
writable by the CPU, a 16-bit counter, and a 16-bit latch readable by the CPU. The load register and latch are
accessed a byte at a time. No I/O pins are dedicated to timer/counter functions. If, for example, timer/counter 1 is
used for input signals only, then IO0 is available for other input or output functions. Timer/counter clock and enable
inputs may be from external pins, or from scaled clocks derived from the system clock; the clock rates of the two
timer/counters are independent of each other. External clock actions occur optionally on the rising edge, the falling
edge, or both rising and falling edges of the input.
Multiple timer/counter input objects may be declared on different pins within a single application. By calling the
io_select() function, the application can use the first timer/counter to implement up to four different input objects. If a
timer/counter is configured to implement one of the output objects, or is configured as a quadrature input object, then
it can not be reassigned to another timer/counter object in the same application program.
Figure 3.1 FT Smart Transceiver Timer/Counter External Connections
System Clock
Divide Chain
Timer/Counter 1
Timer/Counter 2
IO10
IO9
IO8
IO0
IO1
IO2
IO3
IO4
IO5
IO6
IO7
mux
20 mA Sink Capability Programmable Pull-Up Capability