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.
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On 50 Hz systems (commonly, though incorrectly known as "PAL"), the bits that are widely used and interpreted as CGMS-A are not named as such, and are added at the end of an existing signalling standard originally created for the PALplus video format (but still in common use in Europe in standard PAL video) called Widescreen signaling.
CGMS-A |
In analog television systems the vertical blanking interval can be used for datacasting (to carry digital data), since nothing sent during the VBI is displayed on the screen; various test signals, time codes, closed captioning, teletext, CGMS-A copy-protection indicators, and various data encoded by the XDS protocol (e.g., the content ratings for V-chip use) and other digital data can be sent during this time period.