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network. This feature is useful because it
minimizes the need for human intervention.
When a value placed in the Tentative ID
Register matches the Node ID of another node
on the network, the TENTID bit is set, telling the
software that this NODE ID already exists on the
network. The software should periodically place
values in the Tentative ID Register and monitor
the New Next ID bit to maintain an updated
network map.
OSCILLATOR
The COM20020 contains circuitry which, in
conjunction with an external parallel resonant
crystal or TTL clock, forms an oscillator.
If an external crystal is used, two capacitors are
needed (one from each leg of the crystal to
ground). No external resistor is required, since
the COM20020 contains an internal resistor.
The crystal must have an accuracy of 0.020%
or better.
The XTAL2 side of the crystal may be loaded
with a single 74HC-type buffer in order to
generate a clock for other devices.
The user may attach an external TTL clock,
rather than a crystal, to the XTAL1 signal. In
this case, a 390Ω pull-up resistor is required on
XTAL1, while XTAL2 should be left
unconnected.