EPCs (Embedded PCs) are complete computers built on a single PCB, and take advantage of PC-compatible architecture as there is extensive knowledge and resources available. What makes EPCs different from Desktop or Notebook PCs are the specialized form factor, ruggedized mechanical design, extended operating temperature range (industrial temperature range, usually -40°C to +85°C or +105°C), low power consumption (vs. Desktop PCs), extended product/platform lifetime, vast range of software tools, and very specific technical support. EPCs also tend to have higher power density and, as such, the requirements for compact signal processing and power conversion solutions are usually at the top of the list. Plug-in cards for these systems are most often high-performance graphics cards (with graphics co-processors), high-end RAID controllers, and specialized I/O cards such as data acquisition and Digital Signal Processor (DSP) boards.
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The main EPC components are the CPU (single or dual), memory, chipset (MCH and ICH), Graphics Processor Unit (GPU), audio, and high-speed ports such as PCI Express, Ethernet, and USB. The trend is for PCI to be no longer supported on motherboards but there will still be the need for backward compatibility to PCI. Once this transition is complete, PCIe-to-PCI bridge ICs, as offered by Texas Instruments, will be most useful. Additionally, most EPC motherboards offer on-board support for IDE/SATA disk drives with RAID as well as for keyboard/mouse. In applications where graphics and video are not needed, the GPU and display may not be included in the system as in the prevalent case where the EPCs are part of a rack system with no video requirements. However, when used in industrial process control systems, EPCs use displays and, quite often, leverage touch panel Human-Machine Interface (HMI) control.
There are generally two choices for EPC systems: Single Board Computers (SBCs) and Computers-On-Modules (COMs).
- SBCs, which enable the shortest development time, are off-the-shelf compact motherboards with I/Os on board, and because of their power density, low power CPUs are almost always used.
- COMs (unlike SBCs) usually lack the standard connectors for any I/O to be attached directly to the board. Instead, I/Os are bussed out to connectors on the board and, in turn, plug into a main board. They provide the most flexible design, highest scalability, and customization with a range of CPUs, memory, and I/Os available. COMs are offered in many form factors including ETX, XTX, and COM Express.
Main subsystem components:
- Central Processing Unit (CPU) - The CPU handles all the complex processing functions (complex arithmetic, video coding, graphic processing) and interfaces directly with the chipset.
- Chipset - Interfaces with and controls the memory, graphics, and I/O traffic to and from the CPU. In many of today's EPCs there are either two chips, the Graphics and Memory Controller Hub (GMCH) and the I/O Controller Hub (ICH). In newer EPC platforms, the memory controller is integrated into the CPU, and there is only one other controller chip in addition to the CPU, which is sometimes called System Controller Hub.
- Memory - Stores the application software and data files. Most often SDRAM (1.8 V DDR2 SDRAM or 1.5 V DDR3 SDRAM) is used on board to enable shorter read/write access times requiring a dedicated power converter, but Flash memory is also sometimes used.
- PCI Express Bus - PCIe was designed as a much faster serial interface to replace PCI/PCI-X and Advanced Graphics Port (AGP) interfaces for computer expansion cards and graphics cards, respectively. The PCIe 1.x bus runs at 2.5 GHz and uses 8b10b encoding for error detection (10 clock cycles to transmit one byte); equivalent to a data rate of 250 MB/s. The connection between a PCIe 1.x card and motherboard may consist of between one and 32 lanes giving a maximum transfer rate of 8 GB/s in each direction. PCIe 2.0 doubles the data rate of each lane to 500 MB/s, and is backward compatible with PCIe 1.x in both physical interface and software allowing older cards to work in EPCs fitted with PCIe 2.0. PCIe 3.0, which is currently in definition, doubles the data rate yet again to 1 GB/s and will also be backward compatible with existing PCIe implementations.
- Ethernet - Enables the EPC to connect to the LAN for networking capability.
- USB - Multiple USB ports are typically provided to enable connectivity to various peripherals such as external storage.
- Power Conversion - EPCs use line power (AC/DC adaptors) or battery power for the main power input. Popular DC power input voltages for EPCs are 5V, 12V, 16V, 19V, and even 24V or 28V.
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