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Pioneer PX-7 Service Manual
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(1)Video control circuit• EXTV reading(T) EXTV is a status signal indicating the presence/absence of an external video signal (L levelwhen present)® EXTV is read by the CPU when bit 7 of theVCON register is read.(3) Example:The VCON register contents are placed inregister A byLD A, (7FFFH)and the EXTV status is indicated by D7.• EXTV readingWA V7//////A Y7777,Fig. 13-16 EXTV reading timing• VOVLY generation(T) The VOVLY control signal used in computermode and superimpose/extemal video modeswitching is only switched to L when anexternal video signal is applied (EXTV at L)with L written in bit 0 of the VCON register.(2) When RESET is switched to L, VOVLY isswitched to H with point E in Fig. 13-19at H.(3) The DO status (L or H) is latched by theleading edge of VCONW, and the Q output (E)is ORed with EXTV to obtain the VOVLYsignal.VOVLY generation• INTEXV generation(1) The INTEXV and INTEXV signals are generat-ed when the external video signal stops insuperimpose or external video mode. INTEXVserves as the CPU interrup signal, and INTEXVserves as the corresponding status signal.(2) Since point A is at H and point B at L whenRESET is applied, point C and point D areswitched to H, resulting in INTEXV also beingswitched to H. And when the VCON register isread, INTEXV=0 is obtained from bit 0.(3) When EXTV is changed from L to H (that is,when the external video signal is stopped),point C is kept at L from the leading edge ofthe next 0 up to the trailing edge of the next 0after that, thereby resulting in point D becom-ing L and point D H.(4) If point E is L (designation of superimpose orexternal video mode), INTEXV is switched toL to generate a CPU interrupt.(5) INTEXV=1 is obtained from bit 0 when theVCON register is read during the interruptprocessing routine, thereby indicating that theinterrupt is from INTEXV. After completingthe read operation, point D is changed to Hand point D to L by the VCONR leading edge,resulting in INTEXV being reverted to H tocancel the interrupt.• INTEXV generationFig. 13-18 INTEXV generation timing |
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