| 摘要 |
A circuit for converting a TV receiver to operate in accordance with the system associated with received signals, there being either F or F' scan lines in a field, with F<F', includes a counter driven by pulses each representative of one end of a raster scan line, and having M stages, with F and F'<M<2F and 2F'. There is also means to preload the counter selectively with a count of R or R', where (M-2R)=F and (M-2R')=F'. Wide window means detects when a field sync pulse is within a window including the (M-R)th and (M-R') stages, and, in response, the counter, initially, is preloaded with R'. Decision logic means then detects whether a field sync pulse occurs after the Kth stage, with K=M-[R+R']/2, when R' is continued to be preload; or occurs before the Kth stage, when R subsequently is preloaded; and the required TV receiver conversion is completed.
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