Signalling
CEA-608-B specifies meaning of the 7-bit field placed on the data lines. The bits 4 and 3 contain the CGMS-A values, the bits 2 and 1 contain the Analog Protection System (APS) value, the bit 0 is the Analog Source Bit (ASB) specifying if the signal originates from a pre-recorded material, bits 5 and 6 are reserved.
CGMS-A is signalled by 2 bits in the vertical blanking interval (VBI) signal of analog television broadcasts according to the following matrix:
| 0 | 0 | CopyFreely | Unlimited copies may be made of the content. |
| 0 | 1 | CopyNoMore* | One generation of copies has already been made; no further copying is allowed. |
| 1 | 0 | CopyOnce | One generation of copies may be made |
| 1 | 1 | CopyNever | No copies may be made of the content. |
*CopyNoMore was not a part of the original standard. The 0,1 value originally was "Reserved".
Read more about this topic: CGMS