The software pack Keil:ARM_Compiler contains several example projects that show how to do I/O retargeting. Use Pack Installer to copy the projects to your working folder. Build the selected project and enter a debug session.

The following example projects are available:

Example Project	Description
Retarget Input via Keyboard and Output via Display	Shows how to use a USB keyboard for STDIN and a TFT LCD for STDOUT.
Retarget Output via ITM	Shows how to use ITM for STDOUT.
Retarget Input and Output via UART	Shows how to use a U(S)ART for STDOUT.
Retarget STDOUT via Event Recorder	µVision simulator example that shows how to use Event Recorder for STDOUT.