VIC-1011A RS232C adapter
The VIC-1011A RS232C (terminal type) adapter is a device that plugs into the VIC-20's user port. It allows many peripherals (manufacturered by Commodore or a third party) which adhere to the industry standard RS232 communications protocol to be connected to the VIC-20. The VIC-1011A is a "terminal type" interface which outputs true RS232 voltages. Because of this it can be used to connect a RS232 modem to the VIC-20.
Like most of the "utilitarian" VIC-20 plug-in peripherals that Commodore produced, the VIC-1011A conforms to the brown & silver colour scheme.
See also the VIC-1011B RS232C adapter.