REV. B

AD7870/AD7875/AD7876

–10–

Figure 10. Mode 1 Timing Diagram, Byte or Serial Read

its

BUSY function. BUSY goes low at the start of conversion,

stays low during the conversion and returns high when the con-

version is complete. It is normally used in parallel interfaces to

drive the microprocessor into a WAIT state for the duration of

conversion.

Figure 11 shows the Mode 2 timing diagram for the 12-bit par-

allel data output format (12/

8/CLK = +5 V). In this case, the

ADC behaves like slow memory. The major advantage of this

interface is that it allows the microprocessor to start conversion,

WAIT and then read data with a single READ instruction. The

user does not have to worry about servicing interrupts or ensur-

ing that software delays are long enough to avoid reading during

conversion.

Figure 11. Mode 2 Timing Diagram, 12-Bit Parallel Read

The Mode 1 timing diagram for byte and serial data is shown in

Figure 10.

INT goes low at the end of conversion and is reset

high by the first falling edge of

CS and RD. This first read at the

end of conversion can either access the low byte or high byte of

data depending on the status of HBEN (Figure 10 shows low

byte only for example). The diagram shows both a noncontinu-

ously and a continuously running clock (dashed line).

MODE 2 INTERFACE

The second interface mode is achieved by hard wiring

CONVST

low and conversion is initiated by taking

CS low while HBEN is

low. The track/hold amplifier goes into the hold mode on the

falling edge of

CS. In this mode, the BUSY/INT pin assumes