AD7845

REV. B

–11–

Figure 23 and 24 are the interface circuits for the Z80 and

MC6809 microprocessors. Again, these use the same basic

format as the 8085A interface.

Figure 23. AD7845 to Z80 Interface

Figure 24. MC6809 Interface

DIGITAL FEEDTHROUGH

In the preceding interface configurations, most digital inputs to

the AD7845 are directly connected to the microprocessor bus.

Even when the device is not selected, these inputs will be con-

stantly changing. The high frequency logic activity on the bus

can feed through the DAC package capacitance to show up as

noise on the analog output. To minimize this digital feedthrough

isolate the DAC from the noise source. Figure 25 shows an

interface circuit which uses this technique. All data inputs are

latched from the busy by the

CS signal. One may also use other

means, such as peripheral interface devices, to reduce the digital

feedthrough.

Figure 25. AD7845 Interface Circuit Using Latches to

Minimize Digital Feedthrough