Hardware Reference
In-Depth Information
PRINT FILTER SPEC
PRINT FILTER LABEL
LOOP UNTIL LAST FILTER
END
Most of the statements within the algorithm are coded as procedures. As an
example, the procedure which prompts the user for values which will be used
to set the system parameters (
GET SYSTEM PARAMETERS
) is itself described by
the algorithm:
PROCEDURE GET SYSTEM PARAMETERS
GET INITIAL FREQUENCY
GET FINAL FREQUENCY
GET FREQUENCY INCREMENT
GET RF LEVEL
END PROCEDURE
Having decomposed each procedure, it is possible to translate each structured
English statement into equivalent BASIC program statements. As an example,
GET INITIAL FREQUENCY
could be coded (in minimal form) as follows:
INPUT "Start frequency (kHz) "; start
In practice, a range check is desirable on this input since the normal range of
start frequencies will lie within the range 400-450 kHz. The final code for
GET
INITIAL FREQUENCY
was therefore:
DO
INPUT "Start frequency (kHz) "; start
LOOP WHILE start < 400 OR start > 450
A speech enunciator
The client is a manufacturer of 'user-friendly' data entry devices and requires a
low-cost system capable of recording and playing back analogue speech signals.
This system will then be incorporated into an existing terminal based on a PC-
compatible motherboard and fitted with a solid-state disk. The prototype speech
enunciator card is shown in Photo 12.1.
Specification
The client requires that speech of up to 30-s duration and nominal bandwidth
6 kHz be available within the system. The speech signal (input from a micro-
phone) is to be converted to digital information and stored in one or more data
files within a reserved partition on the hard disk. The speech data is then to be
made available for replay (as required) by the terminal control program.
Hardware
This system requires a fast A/D and D/A interface together with additional
analogue signal filtering in order to reduce the effects of aliasing. No card of
