FPGA basic knowledge and development trend (part2)

Because LUT-based FPGAs are highly integrated, with device densities ranging from tens of thousands to tens of millions of gates, they can perform extremely complex timing and logic combination logic functions, so they are suitable for high-speed, high-density high-end digital The field of logic circuit design. Its components mainly include programmable input/output units, basic programmable logic units, embedded SRAM, rich routing resources, underlying embedded functional units, embedded dedicated units, etc. The main design and manufacturer have Xilinx, Altera, Companies such as LatTIce, Actel, Atmel, and QuickLogic, the largest of which is Xilinx, USA, have more than 50% of the market share of the programmable market, more than the combined market share of all other competitors.

The FPGA is set by the program stored in the on-chip RAM, so the on-chip RAM needs to be programmed during operation. Users can use different programming methods according to different configuration modes.

When power is applied, the FPGA chip reads the data in the EPROM into the on-chip programming RAM. After the configuration is completed, the FPGA enters the working state. After the power is turned off, the FPGA is restored to a white chip, and the internal logic relationship disappears. Therefore, the FPGA can be used repeatedly. FPGA programming requires no dedicated FPGA programmer, just a generic EPROM, PROM programmer. In this way, the same FPGA, different programming data, can produce different circuit functions. Therefore, the use of FPGAs is very flexible.

Xilinx Spartan-3 Series FPGA

Figure 2-2 The widely used Xilinx Spartan-3 series FPGA

As mentioned earlier, the FPGA is set by the on-chip RAM to set its working state, so the on-chip RAM needs to be programmed during operation. Users can use different programming methods according to different configuration modes. There are five common configuration modes for Xilinx FPGAs: main string mode, slave string mode, Select MAP mode, Desktop configuration, and direct SPI configuration.

Currently, the two companies with the highest FPGA market share, Xilinx and Altera, are based on the SRAM process and need to be connected to an off-chip memory to save the program. At power-on, the FPGA reads the data in the external memory into the on-chip RAM. After the configuration is completed, it enters the working state. After the power is turned off, the FPGA returns to the white chip, and the internal logic disappears. In this way, the FPGA can be used not only repeatedly, but also without a special FPGA programmer. It only needs a general-purpose PROM and PROM programmer. Actel, QuickLogic and other companies also offer anti-fuse technology FPGAs, which have the advantages of radiation resistance, high and low temperature resistance, low power consumption and high speed. They are widely used in military and aerospace applications, but such FPGAs cannot be repeatedly erased. At the beginning of development, it is troublesome and expensive. LatTIce is the inventor of ISP technology and has some features in small-scale PLD applications. Early Xilinx products generally did not involve military and aerospace-grade markets, but a number of products have entered this category.

FPGA chip internal structure

Figure 2-3 Internal structure of the FPGA chip

FPGA Chip Architecture The current mainstream FPGAs are still based on look-up table technology, which has far exceeded the basic performance of previous versions and integrates hard-core (ASIC-type) modules for common functions such as RAM, clock management and DSP. As shown in Figure 2-3 (Note: Figure 2-3 is just a schematic diagram. In fact, each series of FPGAs has its corresponding internal structure). The FPGA chip is mainly completed by 6 parts: programmable input and output unit Basic programmable logic unit, complete clock management, embedded block RAM, rich routing resources, embedded low-level functional units and embedded dedicated hardware modules.

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