Hardware Reference
In-Depth Information
Photo 12.1
Prototype speech enunciator card
Figure 12.6
Simplified block schematic of the prototype speech enunciator
this type is available 'off the shelf ' and thus a board must be prototyped from
scratch. The prototype is built using a full-size ISA prototyping card which
incorporates the necessary bus interface logic (see Chapter 2). Figure 12.6
shows a simplified block schematic of the hardware arrangement.
The need for A/D and D/A conversion can be realized by using a complete
analogue I/O system in the form of the Analogue Devices AD7569. This unit
offers 8-bit resolution (adequate for this simple speech application) coupled
with a 2
ยต
s ADC track/hold time, and on-chip band-gap 1.25 V voltage ref-
erence. The device is fabricated in linear-compatible CMOS (LC
2
MOS) and
is supplied in a 24-pin 'skinny' DIP package. The internal architecture of the
AD7569 is shown in Figure 12.7 while the simplified circuit of the prototype
interface card is shown in Figure 12.8.
