BECKHOFF BC7300 - Manual (Page 40)

Bus Terminal Controller
40 BC7300
Allocated flags area
The allocated flags area offers a variety of further additional functions and
diagnostic facilities.
Cycle tick counter
The cycle tick counter starts at address %MB504. Each tick corresponds to
about 1 ms. The counter has 32 bits, and can also be written from the PLC
in order to set it to zero or to some other particular value.
Fieldbus diagnostics
Fieldbus diagnostics are located at flag words 508 and 509.
%MX508.0
"TRUE" watchdog time elapsed
The bit is set to "1" if a write telegram has been processed and no new write
telegram is sent to the Bus Terminal Controller within the watchdog time.
No other bits have any function.
K-Bus diagnostics K-Bus diagnostics are located at flag words 510 and 511.
%MX510.0
"TRUE" K-Bus error
%MX510.1 "TRUE" configuration error
Flag byte
Meaning
%MW508 Bit 0: Fieldbus error
Bits 1-15: reserved
%MW510 Bit 0: K-Bus error
Bit 1: Configuration error
Bits 2-15: reserved
Data acces via Modbus
From the firmware B4 is it as well possible to access directly reading and
writing on the flag area. This access does not trigger the watchdog. That
means values which are written in this range, remain as well after a
watchdog error set.