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AD7828CQ 데이터시트(PDF) 9 Page - Analog Devices |
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AD7828CQ 데이터시트(HTML) 9 Page - Analog Devices |
9 / 16 page AD7824/AD7828 REV. F –9– MODE 0 Figure 14 shows the timing diagram for Mode 0 operation. This mode can only be used for microprocessors that have a WAIT state facility, whereby a READ instruction cycle can be extended to accommodate slow memory devices. A READ operation brings CS and RD low, which starts a conversion. The analog multiplexer address inputs must remain valid while CS and RD are low. The data bus (DB7–DB0) remains in the three-state condition until conversion is complete. There are two converter status outputs on the AD7824/AD7828, interrupt ( INT) and ready (RDY), which can be used to drive the microprocessor READY/WAIT input. The RDY is an open-drain output (no internal pull-up device) that goes low on the falling edge of CS and goes high impedance at the end of conversion when the 8-bit conversion result appears on the data outputs. If the RDY status is not required, the external pull-up resistor can be omitted and the RDY output tied to GND. The INT goes low when conversion is complete and returns high on the rising edge of CS or RD. MODE 1 Mode 1 operation is designed for applications where the micropro- cessor is not forced into a WAIT state. A READ operation takes CS and RD low, which triggers a conversion (see Figure 15). The multiplexer address inputs are latched on the rising edge of RD. Data from the previous conversion is read from the three-state data outputs (DB7–DB0). This data may be disregarded if not required. Note that the RDY output (open drain output) does not provide any status information in this mode and must be connected to GND. At the end of conversion, INT goes low. A second READ operation is required to access the new conversion result. This READ operation latches a new address into the multi- plexer inputs and starts another conversion. INT returns high at the end of the second READ operation, when CS or RD returns high. A delay of 2.5 µs must be allowed between READ operations. CS RD ANALOG CHANNEL ADDRESS RDY INT DATA tCSS tAS tRDY tCRD tACC2 tDH tINTH tAH tAS tP tCSS tCSH ADDRESS VALID ADDRESS VALID DATA VALID HIGH IMPEDANCE Figure 14. Mode 0 Timing Diagram CS RD ANALOG CHANNEL ADDRESS INT DATA tCSS tAS ADDRESS VALID OLD VALID ADDRESS VALID NEW VALID tCSH tAH tRD tCRD tINTH tACC1 tDH tACC1 tDH tINTH tAH tAS tP tCSS tRD tCSH Figure 15. Mode 1 Timing Diagram |
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