A Programmable system device (PSD) is a type of integrated circuit manufactured by STMicroelectronics. Meant to be teamed up with a microprocessor or microcontroller, the PSD provides most of the other functions required to implement small applications such as embedded systems.
The PSD provides the following functions:
The entire PSD is reprogrammable using JTAG; this includes the random logic that's configuration is loaded from flash-like memory. If the user provides the correct connections, the device can also be reprogrammed in the field (still using JTAG) in a process known as In-System Programming. The portions of the chip that act as ordinary flash ROM may also be reprogrammed by the application's microcontroller in a process known as In-Application Programming.
PSDs are made in various configurations with varying amounts of ROM, RAM, random logic, and I/O ports.