Annex M (informative) — Video reference distribution

How to bring one video reference to every video module in a system. The reference travels on the 75 Ω coaxial interface of 7.4, behind the panel, from a VID-REF-OUT to each module's VID-REF-IN, and never on a patch cable: a patch jack carries patched signals only (SIG-015), and a module takes or gives the reference at a rear port it claims by kind (V75-010). The reference is black burst or video sync, and the same 75 Ω cabling is what a picture travels on between products; the two are not interchangeable at a VID-REF-IN.

EIS · Video reference in a row: direct links, a PASSTHRU chain, or a star A link, then a chain of VID-REF-PASSTHRU generator VID-REF-OUT module VID-REF-IN · PASSTHRU module VID-REF-IN · PASSTHRU module VID-REF-IN · PASSTHRU one VID-REF-OUT; each PASSTHRU drives the next VID-REF-IN never a patch jack (SIG-015); a PASSTHRU is not an output (V75-013) VID-75 star generator VID-REF-OUT bus board REF-IN, PASSTHRU x n module VID-REF-IN module VID-REF-IN module VID-REF-IN one COAX-IN per output (V75-005) one source per tree (ASM-007) The reference is rear coaxial cabling, wired once: a link suits a few modules, a PASSTHRU chain or a LOOP run suits a row that has them, the star suits many locking to one reference, and BNC takes a facility reference. Jack types may be mixed in a tree; a passive split is never used.

Situation Typical choice
A few modules and a generator with several VID-REF-OUT ports One coaxial link from a VID-REF-OUT to each module's VID-REF-IN; no distributor
Modules with VID-REF-PASSTHRU, in a row A chain: generator VID-REF-OUT to the first module's VID-REF-IN, its VID-REF-PASSTHRU to the next VID-REF-IN, and so on; each PASSTHRU drives one input
Modules with VID-REF-LOOPTHRU One cable run through the loop pairs, the termination switch on at the last module only
Many modules lock to one reference A star: a distributor, usually a bus board that carries the tree (BUS-020), one VID-REF-PASSTHRU per VID-REF-IN
The facility already distributes black burst or tri-level video sync between racks The facility reference at the distributor's VID-REF-IN; BNC jacks suit it
Two rows, one for performance and one for processing A distributor per row, or one coaxial link from the first row's tree to the second row's VID-REF-IN

Jack types may be mixed in a tree, and each output drives one terminated input (V75-005); see 7.4. A VID-REF-PASSTHRU is not a source: a row needs one VID-REF-OUT, or an external reference at a designated input, and the module claims say which ports are which. A module's front patch jacks carry its pictures, ramps, keys, and control (7.2); none of them is the reference, so a patch never changes a module's timing.

Many video modules in use take their video reference on a rear 2 × 7 ribbon header, which is not a port of 7.4; such a header mates a power ribbon socket, so it is one that BUS-011 reaches (6.4), and a product with one lists it on its port list as unclassified, named for what it connects to (Annex N).