QA-VTM User and Service Manual

U502 is a quad SR-latch, that is used to convert pulses to levels. U501 is a 4 bit counter, that is used to stretch the pulse from the 32 MHz clock, so that the pulse width is long enough so that the microcontroller can detect it. The time delay between transmitting a pulse, and receiving the pulse, is about 0.8 to 1.0 ms. With the 32 MHz clock ... ................
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