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DN120 DeviceNet Gateway User’s Manual
Microscan Systems, Inc.
14
If the number of
RX Message
bytes currently in the Receive Buffer is less than the
Maximum
Receive Size
number, then the remaining input bytes are undefined. The gateway can optionally
fill the unused input bytes with a
Pad
character. The
Pad
characters can be added at the
beginning or end of the message.
If configured for
Pre-Delimiter Block Mode
and the
Delimiter
byte is saved, the
Pad
characters
are added either after the last valid message byte (right justification) or before the
Delimiter
byte
(left justification).
If configured for
Post-Delimiter Block Mode
and the
Delimiter
byte is saved, the
Pad
characters
are added either before the first valid message byte (left justification), or after the last valid
message byte but before the
Delimiter
byte (right justification).
Re-sending Received Data
The DN120 gateway can be configured to return received message bytes only once in a Poll
Response message, and return no data (null value) in subsequent Poll Response messages until
new message bytes are received. For the Short_String data type, a null value consists of the
length byte = 0. For the Byte Array data type, a null value consists of no data.
The gateway can also be configured to always return received message bytes in a Poll Response
message. If no new bytes in the Receive Buffer, then the last received bytes are returned. If new
bytes are in the Receive Buffer, then they are returned. The gateway provides
Receive Sequence
Number
or
Handshake Protocol
synchronization options to indicate whether the returned bytes
represent old or new data.
Status
Receive Sequence Number
other input bytes
RX Message Bytes
RX Message bytes
Pad Bytes
1. The are enough message bytes in Receive
Buffer to fill Poll Response.
Poll Response Message Data
RX Message bytes
Pad Bytes
RX Message bytes
undefined
2. The are not enough message bytes in
Receive Buffer to fill Poll Response. Unused
input bytes are undefined.
3. The are not enough message bytes in
Receive Buffer to fill Poll Response. Pad bytes
are added after message bytes.
4. The are not enough message bytes in
Receive Buffer to fill Poll Response. Pad bytes
are added before message bytes.