AD664
Expansion of the scheme employed in Figure 25a results in that
shown in Figure 25c. Here, two AD664s are connected to an
MC6801, providing a total of eight 12-bit, software program-
mable DACs. Again, the three least significant bits of address
are used to select the on-chip registers of the AD664. IOS and
E, as well as a fourth address bit, are decoded to provide the
appropriate CS signals. Four address and five I/O lines remain
uncommitted.
A slightly more sophisticated approach to system expansion is
illustrated in Figure 25d. Here, a 74LS138 (1-of-8 decoder) is
used to address one of the eight AD664s connected to the
MC6801. The three least significant address bits are used to
select on-chip register and DAC. The next three address bits are
used to select the appropriate AD664. IOS and E gate the
74LS138 output.
Figure 25a. Simple AD664 to MC6801 Interface
Figure 25b. Alternate AD664 to MC6801 Interface
Figure 25c. Interfacing Two AD664s to an MC6801
–13–
D
REV.
ADI [ ADI ]
