A Programmable system device (PSD) is a type of integrated circuit

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

 manufactured by STMicroelectronics

STMicroelectronics

STMicroelectronics is an Italian-French electronics and semiconductor manufacturer headquartered in Geneva, Switzerland.While STMicroelectronics corporate headquarters and the headquarters for EMEA region are based in Geneva, the holding company, STMicroelectronics N.V. is registered in Amsterdam,...

. Meant to be teamed up with a microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

 or microcontroller

Microcontroller

A microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Program memory in the form of NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of RAM...

, the PSD provides most of the other functions required to implement small applications such as embedded system

Embedded system

An embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...

s.

The PSD provides the following functions:

• RAM
• Flash ROM
  Read-only memory
  Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
  
  
• A reprogrammable gate array
  Gate array
  A gate array or uncommitted logic array is an approach to the design and manufacture of application-specific integrated circuits...
  
   for address decode
  Memory mapping
  In computing, memory mapping may refer to:* Memory-mapped file, also known as mmap* Memory-mapped I/O, an alternative to port I/O; a communication between CPU and peripheral device using the same instructions, and same bus, as between CPU and memory...
  
  , input/output
  Input/output
  In computing, input/output, or I/O, refers to the communication between an information processing system , and the outside world, possibly a human, or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it...
  
   functions, and random logic

The entire PSD is reprogrammable using JTAG

JTAG

Joint Test Action Group is the common name for what was later standardized as the IEEE 1149.1 Standard Test Access Port and Boundary-Scan Architecture. It was initially devised for testing printed circuit boards using boundary scan and is still widely used for this application.Today JTAG is also...

; 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

In-System Programming

In-System Programming is the ability of some programmable logic devices, microcontrollers, and other programmable electronic chips to be programmed while installed in a complete system, rather than requiring the chip to be programmed prior to installing it into the system.The primary advantage of...

. 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.