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3.3 Reference and Clock An internal bandgap circuit is used to generate all necessary reference voltages and currents. The on-chip crystal oscillator is used to generate 20MHz reference clocks for the internal circuits. For precision clock generation, a 20MHz-30 100ppm crystal should be used. And two 30pF load capacitors should be connected from X1 and X2 to ground, respectively. If an external clock source is used, it should be applied to X1 while X2 is grounded.
Common I O for reduced pin count Four operation modes shift left shift right parallel load and store Separate continuous inputs and outputs from Q0 and Q7 allow easy cascading Fully synchronous reset TRI-STATE outputs for bus oriented applications
In operation, the HCPL-7860/ HCPL-786J Isolated Modulator (optocoupler with 3750 VRMS dielectric withstand voltage rating) converts a low- bandwidth analog input into a high-speed one-bit data stream by means of a Sigma-Delta (− ∆) over-sampling modulator. This modulation provides for high noise margins and excellent immunity against isolation-mode transients. The modulator data and on-chip sampling clock are encoded and transmitted across the isolation boundary where they are recovered and decoded into separate high-speed clock and data channels.