7.
Interfacing
to computer
It is important to read memory contents of ITDL through a computer for future improvement and further expansions of the system by software modifications. Therefore, to facilitate that and to download the stored data to a computer, an RS232 serial Driver/Receiver is associated to the system. Hence, analysis report of telephone calls together with call charges can be calculated and printed with an application software.
Fig.
5 Illustration of computer
interfacing to ITDL
Fig.5
depicts the link between Z80 PIO and RS232 serial port of computer. The
capacitors C7, C8, C9 and C10 form a voltage-doubling network together with
internal converters of MAX232 to satisfy its operational conditions.
One
pair of Driver/Receiver has been chosen for the application and PA6 and PA7 of
Z80 PIO establish transmitter and receiver path respectively. Further, 9 pin
serial port of the computer is connected via a cable to the ITDL serial port as
shown in the diagram. The transistor T1 and associated LED circuit provide
visual indication of proper connection between ITDL and computer while blinking
LED signifies that the data are being downloaded.