snap ethernet-based i/o units protocols and programming guide

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CHAPTER 4: USING THE IEEE 1394-BASED PROTOCOL
Write Response Packet (Brain➞PC)
When the brain receives the Powerup Clear, it sends a Write Response packet back to the host
PC acknowledging receipt. In binary notation, the response packet looks like this:
The rcode parameter contains the ACK or NAK for the transaction. The 0 in this example indicates
an ACK.
In hex, the packet looks like this: 000004200000000000000000. The 0 shown in bold type is the
ACK in the rcode.
See “Error Codes” on page 98 for information on what to do if you receive a NAK.
Configuring
destination_ID tl rt tcode pri
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0
source_ID rcode reserved
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
reserved
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
SNAP Ethernet-based brains can recognize the presence and type of an analog module on the
rack, but the values for each of the points must be configured if they do not match the default for
that module type. For example, the brain can report that a SNAP-AITM module is in position 4,
but if the points are anything other than the default value of ±150 mV, you must configure them
by writing configuration codes to the points. Module types and default values are shown on
page 18.
Digital modules and empty positions are reported the same by the brain: they are assumed to be
digital input modules. If a position contains a digital output module, you must configure the
points as outputs.
Configuring I/O Point Types—Write Quadlet Request Packet (PC➞Brain)
Suppose you have a digital output module in position 0 on the rack. Since the brain cannot
distinguish a digital module from an empty position, you need to configure the module’s four
output points (points 0–3) as outputs. You configure them by writing to each one’s Point Type
address in the “Analog and Digital Point Configuration Information—Read/Write” area of the
memory map. On page 125 you can see this area of the map.
84 SNAP Ethernet-Based I/O Units Protocols and Programming Guide