I/O Transceivers & Buffers
MAX 7000B devices are the only product-term-based programmable logic devices (PLDs) that support GTL+ and SSTL-2 and SSTL-3 standards. These standards are common in processor interfaces, backplane drivers, and synchronous dynamic random access memory (SDRAM) interfaces.
Many of these applications call for the use of product-term-based PLDs to implement control and decode logic. Discrete I/O drivers or transceivers are usually required to convert the signals from GTL+ or SSTL-2 and SSTL-3 signals to LVCMOS or LVTTL.
Because MAX 7000B devices can directly interface with these advanced I/O standards, discrete drivers are not required when designers use MAX 7000B devices. Using a single MAX 7000B device, a designer can incorporate logic in high-performance designs and at the same time replace external drivers. This integration eliminates additional chip-to-chip delays and saves valuable board space. See Figure 1.
Figure 1: MAX 7000B Device
MAX 7000B devices can replace discrete GTL+ and SSTL-2 and SSTL-3 drivers that are readily available from many semiconductor manufacturers, as long as requirements for the number of I/O pins and the current drive are met. The number of I/O pins is the limiting factor when LVTTL or LVCMOS is the output standard, whereas the current drive is the limiting factor when GTL+ or SSTL-2 and SSTL-3 is the output standard.
As shown in Figure 2, MAX 7000B devices contain two I/O banks and each I/O bank has its own VCCIO pins. Each bank can independently support a different I/O standard. Within a bank, any one of the terminated standards can be supported.
Figure 2: I/O Banks in MAX 7000B devices
Each MAX 7000B device also has two VREF pins that can each be set to separate VREF levels. Any I/O pin that uses one of the voltage-referenced advanced I/O standards (GTL+, SSTL-2, SSTL-3) can use either of the two VREF pins.
For more technical details on how to integrate I/O transceivers and buffers, refer to AN 293: Using MAX 7000B Devices to Replace I/O Drivers.
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