Using S300 virtual input to release motor brake via fieldbus

There is an undocumented parameter in the S300, SOFTIN. Bit 0 of this variable is for input 5, bit 1 for input 6,..., . If you set SOFTIN = 1, IN5 will return 1.
To operate the brake set IN5MODE = 32.
With SOFTIN = 1 the (virtual) input 5 is activated and the brake opens.

The parameter SOFTIN is DPR object number 78 or Profibus PNU 1678. That allows you to operate the brake via DeviceNet or Profibus. Remember for For PNU 1678 set IND = 1.