Field responsive vertical pulse generator

摘要

In an NTSC television system there are an odd number (262.5) of horizontal lines in each field. This relationship causes a 50% duty cycle horizontal rate signal (H) to be high during one specific horizontal half line in one field and low for that same horizontal half line in the other field. A 2H rate signal is normally divided by 525 with counters to obtain a field rate. The outputs of the counters are combined with a regenerated horizontal rate signal (H) to generate a plurality of unique addresses. This provides a mapping for each field to within a half horizontal line resolution. These addresses can be decoded by a programmable logic device or other devices to define half, single or groups of horizontal lines in one or both fields.