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This directory contains the device entries for the dual chain
Maxbotix ultrasonic range sensor interface.


HARDWARE
The Maxbotix range sensor interface supports two chains of Maxbotix
range sensors.  The idea of a 'chain' is that you give a start strobe
to the first sensor on the chain and as it is reporting its distance
it triggers the next sensor in the chain.  The purpose of a chain is
to make sure only one sensor is emitting at a time and to reduce the
overall number of control pins required.
   The ultrasonic pings are sent out sequentially so that they do
not interfere with each other.  Each chain can have as many as eight
sensors.
   Pin 2 (or 10) is the start strobe for the first chain.  Pin 4 (or
12) is the PWM input for the first chain.  The start strobe and PWM
input for the second chain are on pins 6 and 8, or on pins 14 and
16, depending on which peripheral slot is used.


DEVICE NODES
The device interfaces include a configuration device node and a read-
only device node that gives the distances reported by the sensors.

.../config
   A comma separate pair of numbers that give the number of sensors
on each of the two chains.  The first number is the quantity of 
sensors on chain A, and the second number is the quantity of sensors
on chain B.  The configuration line is terminated by a newline.

.../distance
   The distance reported by each sensor as the readings come in.
The distance device node is a broadcast device and file descriptors
for it will work with the select() statement.  The output line has a
character, 'A' or 'B', to indicated the chain, a single digit to give
the sensor position on the chain, and the reported distance distance
in units of one-tenth of an inch.  The fields are comma separated and
terminated by a newline.  A distance of zero indicates that the sensor
is not connected or is not responding.
   Typical output from the distance device node might appear as:
        A, 0, 1055
        A, 1, 55
        A, 2, 0
        B, 0, 1848
        B, 1, 4650
        A, 0, 1094