Echelon FT 3150 Smart Transceiver - Manual (Page 23)

FT 3120 / FT 3150 Smart Transceiver Data Book 17
Input/Output
Table 2.7 External Memory Interface Pins
The preferred method of interfacing the FT Smart Transceiver to another MPU is through the 11 I/O pins using a
serial or parallel connection, or through a dual-ported RAM device such as the Cypress CY7C144, CY7C138, or
CY7C1342. There are pre-defined serial and parallel I/O models for this purpose which are easily implemented using
the Neuron C programming language, or the short stack or MIP firmware can be used to simplify the interface. For
more details of dual-ported RAM interfacing, see Appendix B of the L
ON W ORKS Microprocessor Interface Program
User’s Guide (Echelon 078-0017-01).
Input/Output
Eleven Bidirectional I/O Pins
These pins are usable in several different configurations to provide flexible interfacing to external hardware and
access to the internal timer/counters. The logic level of the output pins may be read back by the application processor.
See Section 6 for detailed electrical characteristics.
Pins IO4 – IO7 have programmable pull-up current sources. They are enabled or disabled with a compiler directive
(see the Neuron C Reference Guide). Pins IO0 – IO3 have high current sink capability (20 mA @ 0.8 V). The others
have the standard sink capability (1.4 mA @ 0.4 V). All pins (IO0 – IO10) have TTL level inputs with hysteresis.
Pins IO0 – IO7 also have low level detect latches.
Two 16-Bit Timer/Counters
The timer/counters are implemented as a load register writable by the processor, a 16-bit counter, and a latch readable
by the processor. The 16-bit registers are accessed 1 byte at a time. Both the FT 3120 and FT 3150 Smart
Transceivers have one timer/counter whose input is selectable among pins IO4 – IO7, and whose output is pin IO0,
and a second timer/counter with input from pin IO4 and output to pin IO1 (Figure 2.7). 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.
Pin Designation Direction Function
A0 – A15 Output Address Pins
D0 – D7 Input/Output Data Pins
E Output Enable Clock
R/W Output Read/Write Select Low