ABB AC 800M

Section 2 Transmission Technology MBP cycle time calculation
3BDS009029R5001 B 39
polarized with respect to device power. These devices are designed so that signal
polarity and power polarity are the same. Connecting the +DC to the (+) terminal
automatically insures correct signal polarity. Non-polar bus powered field devices
accept both signal and power of either polarity.
MBP cycle time calculation
The PROFIBUS-PA data telegrams of the MBP transmission is very similar to
asynchronous RS-485 transmission. While the bytes are transmitted asynchronously
in the form of UART characters over the RS 485 line, the transmission on the MBP
segments is bit synchronous. Here, the telegram is additionally supplied with the
preamble and the start and end delimiter.
Fieldbus Data Link (FDL) defines the following telegrams:
• Telegrams without data field (6 control bytes)
• Telegrams with one data field of fixed length (8 data and 6 control bytes)
Figure 7. MBP data telegram