Performance Motion Devices PR8358120, User Manual

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Accessing Card Resources
58
Prodigy/CME PC/104 User’s Guide
3
Figure 3-1:
Outgoing and
Returning PRP
header formats
The majority of communications to/from the host controller and the Prodigy/CME PC/104 card use the PRP header.
Exceptions are ‘low-level’ communications sent or received directly from the Serial, CANbus, or Ethernet ports. See
Section
3.2, “Accessing the Communications Ports,” on page 59 for more information.
PRP header field descriptions:
Version - This two bit field encodes the version of PRP being used. The value of this field for the Prodigy/CME
PC/104 card should always be 1 (binary 01) unless documentation included with your Prodigy/CME PC/104 card
indicates otherwise.
Status code - For PRP commands being sent out, this 2-bit field should contain the value 2. When received, a return
value of 0 indicates that this message is a normal response to an outgoing PRP command, a return value of 1 indicates
that an error occurred during PRP command processing, and a value of 3 indicates that this is an asynchronous event
message originated by the Prodigy/CME card or by a device attached to the card. Each of these different response
status codes may have information loaded in the PRP message body. See the
Prodigy/CME Programmer’s Reference for
more information.
Action - This 4-bit field contains an action identifier that is used to process PRP messages. See Section 3.1.3, “PRP
Actions,” on page 59 for a summary of the PRP actions supported by the Prodigy/CME PC/104 card. This field is
not used in the return PRP header.
Resource - This 3-bit field encodes the specific resource being addressed. See the table in Section 3.1.2, “PRP
Resources,” on page 59 for the complete resource map of the Prodigy/CME PC/104 card. This field is not used in
the return PRP header.
Address - This 5-bit field encodes the address of the particular resource being communicated to. Fixed addresses
allow on-card resources to be addressed. See the table in Section 3.1.2, “PRP Resources,” on page 59 for a resource
map of these addresses. Automatically assigned addresses are used to access attached devices, and are also used to
create peripheral connections, which are communication ‘conversations’ between the Prodigy/CME PC/104 card and
another device. This field is not used in the return PRP header.
The following sections provide general information on the PRP system. For a detailed description of the PRP header,
resources, and supported actions, see the
Prodigy/CME Programmer’s Reference .
Version Status code Action Resource Address
2 bits 2 bits 4 bits 3 bits 5 bits
Outgoing PRP Header
Return PRP Header
Version Status code Reserved
2 bits 2 bits 4 bits