Performance Motion Devices PR8358120, Руководство пользователя

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Accessing Card Resources
64
Prodigy/CME PC/104 User’s Guide
3
Note that the PRP message to send a Magellan command packet did not use a sub-action code in the message body,
while the
Read
command sent to the dual-ported RAM did. Whether or not a sub-action is required, and what the
codes are for various sub-actions, is action-specific, and sometimes resource-specific. The Prodigy/CME Programmer’s
Reference provides exact message body information for each PRP action and (if applicable) sub-action.
Note also that in this discussion of sending PRP messages to the Prodigy/CME PC/104 card, the specific
communications channel to the card (serial, CANbus, Ethernet) was not discussed. That is because the PRP header
and message body are the same regardless of how transmission occurs. Depending on the network type used, those
varying communication links will send, receive, and process errors for packet communications in different ways, but
from the ‘perspective’ of the PRP system, those message transmission details are handled automatically. This is a very
powerful characteristic of the PRP system, and we will see additional examples of similar ‘access virtualization’ as we
discuss more advanced network topologies.
3.4 Accessing Magellan-Attached
Devices
Section 3.2.1, “Peripheral Connections,” on page 60 provided information on how general purpose messages can be
sent to, or received from, any of the Prodigy/CME PC/104 card’s network ports. This level of low-level access can be
useful to communicate with a wide variety of custom-created or off-the-shelf products that are capable of
communicating on that bus.
If the attached device is a PMD device however, such as an ION or non-/CME Prodigy PC/104 card (PR825xx20
family and PR925xx20 family) then it is possible to integrate these devices into the PRP access network so that they
can be communicated to without using low-level peripheral send and receive commands.
Figure 3-5 on page 65 provides an example of a setup where a Prodigy/CME PC/104 card is connected via Ethernet
to a host controller, and where a second non-CME Prodigy-PC/104 card is attached to the PC/104 bus.
To actually send a PRP command over a serial, CANbus, or Ethernet network, specific protocols must be ob-
served. See Section
3.5, “PRP Communication Formats,” on page 66 for this network-specific (serial, CANbus, or
Ethernet) information.
IONs and non-/CME Prodigy PC/104 cards are referred to as ‘Magellan-Attached’ devices because the network
directly connects to the Magellan Motion Processor, and utilizes the Magellan’s own communication protocols for
receiving commands and returning data along the communication link.