For Xilinx 5 Volt FPGA families XC2000, XC3000, XC4000(E) and XC5200, the input and output threshold level of CCLK is compatible with both 5 Volt TTL and 5 Volt CMOS threshold standards.
Xilinx FPGAs use CMOS transistors, but mimic a BJT-like structure in that outputs drop a threshold on the VOH. Therefore, when CCLK is used as an output, it swings from 0 to 4.0 volts. As an input the CCLK triggers at a threshold of 1.5 Volts. This is compatible with both TTL and CMOS threshold standards:
Thres. TTL CMOS
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VILmax 0.8 1.0
VIHmin 2.0 70% (Vcc)
VOLmax 0.4 0.4
VOHmin 2.4 Vcc - 0.5V
Therefore, CCLK may be used to source or load either TTL or CMOS type external circuitry.
AR# 1519 | |
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日付 | 05/08/2014 |
ステータス | アーカイブ |
種類 | 一般 |