Rockwell Automation 1799-DASCII DeviceNet Serial Interface - Manual (Page 8)

8 DeviceNet Serial Interface Module
Publication 1799-IN012B-EN-P - July 2008
The 1799-DASCII module supports modes of data transfer of the serial buffer that
include the following:
•
Polled I/O
•
Change-of-state I/O
•
Cyclic I/O
•
Explicit Message
Polled I/O
The polled connection is the only way you can send serial output data to the I/O
and I/O devicce. The DeviceNet master initiates the polled connection transfer.
The master sends the 1799-DASCII module its serial output buffer with a record
number and length byte. The 1799-DASCII module monitors the record number for
a change. If the record number changes, the 1799-DASCII module transmits the
data buffer on its serial link. If the record number does not change, the device
does not transmit the data buffer.
After the device has transmitted its data out to the serial link, the 1799-DASCII
module takes any information that is stored in its current serial input buffer and
sends this data to the DeviceNet master. It sends all characters up to and including
the received delimiter, padding only if specified in the parameter object. When the
1799-DASCII module receives a new message with a delimiter or with an overflow
condition without a delimiter), the device increments the receive record, updates
the length byte, and copies the new information from the last receive delimiter into
the buffer. If an overflow occurs, the 1799-DASCII module indicates so in its
receive status bit. The receive status byte also reflects other errors in the device.
Cyclic I/O
The cyclic connection initiates a transmission every time the connection timer
expires. The cyclic connection can only send data from the 1799-DASCII module. If
you need to transmit on the I/O link, the polled connection is necessary. The
polled and cyclic connections can exist simultaneously. The manner in which
cyclic connection reports its data is the same as the polled connection. The cyclic
connections transmit buffer is the same as the polled connections transmit buffer,
so overflows and received delimiters act the same over any connection.
IMPORTANT
Remember to remap the data (if necessary) after setting the sizes, because
many configuration tools automatically unmap data when the connection sizes
change.