PL2303HXD / EA / RA has 8 software controllable “General Purpose Input Output, GPIO” control signals pin, you can use this API to control
-direction: input or output
-logic level: high or low

GPIO Pin define:
1. GP0
2. GP1
3. GP2
4. GP3
5. GP4--RI (*)
6. GP5--DCD(*)
7. GP6--DSR(*)
8. GP7--CTS(*)

(*): In general, serial port control input signals - CTS, DCD, DSR and RI are used as MODEM control signals , However, if the MODEM control signal are not needed, these signal could be used as general-purpose input/output signal(GPIO)

You can download the source code from Prolific web-site, and then develop your own android application

Requirements:
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- USB Device with PL2303HXD, PL2303EA or PL2303RA controller chip
NOTE: PL2303HXA and PL2303XA are not supported (Discontinued Products)
- Android-Powered Device (Tablet/Phones) with USB Host Mode Support
- Android 3.2 and above OS versions