RabbitCore RCM3305, Руководство пользователя

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User’s Manual 141
E.2 Physical Implementation
There are four signaling functions associated with a RabbitNet connection. From the mas-
ter’s point of view, the transmit function carries information and commands to the periph-
eral card. The receive function is used to read back information sent to the master by the
peripheral card. A clock is used to synchronize data going between the two devices at high
speed. The master is the source of this clock. A slave select (SS) function originates at the
master, and when detected by a peripheral card causes it to become selected and respond
to commands received from the master.
The signals themselves are differential RS-422, which are series-terminated at the source.
With this type of termination, the maximum frequency is limited by the round-trip delay
time of the cable. Although a peripheral card could theoretically be up to 45 m (150 ft)
from the master for a data rate of 1 MHz, Rabbit recommends a practical limit of 10 m (33
ft).
Connections between peripheral cards and masters are done using standard 8-conductor
Ethernet cables. Masters and peripheral cards are equipped with RJ-45 8-pin female con-
nectors. The cables may be swapped end for end without affecting functionality.
E.2.1 Control and Routing
Control starts at the master when the master asserts the slave select signal (SS). Then it
simultaneously sends a serial command and clock. The first byte of a command contains
the address of the peripheral card if more than one peripheral card is connected.
A peripheral card assumes it is selected as soon as it receives the select signal. For direct
master-to-peripheral-card connections, this is as soon as the master asserts the select sig-
nal. The connection is established once the select signal reaches the addressed slave. At
this point communication between the master and the selected peripheral card is estab-
lished, and data can flow in both directions simultaneously. The connection is maintained
so long as the master asserts the select signal.