Reset pin, Reset function – Echelon FTXL Hardware User Manual

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FTXL Hardware Guide

Transceiver, this pin is not part of the communications port, and does not

function as a sleep control pin, but acts as in interrupt control pin.

The FTXL LonTalk protocol stack uses the IRQ pin to receive an indication from

the FTXL Transceiver that the network is ready, either for uplink or for

downlink. The FTXL LonTalk protocol stack asserts the IRQ pin high to cause
the interrupt.
The

downlink ready

interrupt allows the FTXL Transceiver to inform the host

when it has read the first byte of the transfer. This interrupt accounts for the

latency of the parallel interface, that is, between a host write for a downlink

transfer and the FTXL Transceiver read for the transfer. This latency is on the
order of 110 microseconds (for an FTXL Transceiver running at 20 MHz), but it

could be longer if the FTXL Transceiver is busy processing an incoming network

frame. The FTXL LonTalk protocol stack initiates a downlink transfer by writing
only the length byte; it then lets the interrupt service routine handle the rest of

the transfer.
The

uplink ready

interrupt is an indication from the FTXL Transceiver that

uplink traffic needs to be transferred. The IRQ pin is asserted only when the

FTXL Transceiver does not own the write token.
The IRQ pin is deasserted during the downlink activity.

Although there are two interrupt cases, there is only a single interrupt request

line. The interrupt type is determined by the FTXL LonTalk protocol stack based
on the state of the FTXL Transceiver and token ownership.

Reset Pin

The RESET~ pin (pin 40) is both an input and an output. As an input, the

RESET~ pin is internally pulled high by a current source acting as a pull-up
resistor. The RESET~ pin becomes an output when any of the following events

occur:

• Software reset
• Watchdog Timer event
• Internal low-voltage inhibit (LVI) circuit detects a low voltage
• RESET~ pin drops below the internal trip point

Important: The Nios II processor must be able to detect changes to and assert
the FTXL Transceiver’s RESET~ pin.

Reset Function

The reset function is a critical operation for any embedded microcontroller. In

the case of an FTXL Transceiver, the reset function plays a key role in the
following conditions:

• Initial V

power up

Reset ensures proper initialization of the FTXL Transceiver.

• V

power fluctuations

Reset manages proper recovery of the FTXL Transceiver after V

stabilizes.