This is the ROM card for the Extended Controller, giving the box EC personality and algorithms. This version of the ROM II card is LCN-compatible. This is the latest ROM II board for the EC prior to the introduction of the Universal Controller.

A flaw in the circuit design of the address decode circuit can cause errors to occur occur in revisions 17 and under of this board (see Honeywell CRM PD 01 C06(A)). Revision 18 and newer resolves the problem.