FW_4.20: Isaac HD firmware 4.20 (builds 625, 631, 1145) and 4.21

Source: C:/Zaxis/Isaac SVN/Release/Firmware/Rabbit Code/IsaacHD_4.20

Files (md5 / source):
  59ade529  IsaacHD_4.20/PLC/Isaac.eds
  bdeba4b6  IsaacHD_4.20/PLC/Isaac_CosBitMsk.eds
  4222fe4f  IsaacHD_4.20/PLC/Isaac_Udts.xlsx
  b8be455e  IsaacHD_4.20/Documentation/Isaac_EtherNetIp.pdf
  b5b015c6  IsaacHD_4.20/PLC/DataType_Referencing.pdf
  04ce0b0a  IsaacHD_4.20/Documentation/ReleaseNotes.pdf

Note: Identical to the IsaacHD_4.20 git repository and to the 'Ethernet IP 4.20.zip' previously given to customers. Adds StartWInterlock (bit 10), SaveDacOnAbort and the CosBitMask parameter.
Note: also covers the '4.20 4Chan' four-channel build (build 924, Nov 2020); use Isaac_CosBitMsk.eds for those testers.
Note: also covers firmware 4.21, whose EDS is byte-identical to Isaac_CosBitMsk.eds; use that file for 4.21 testers.
