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EX256-FTQ100 Datasheet(PDF) 8 Page - Actel Corporation |
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EX256-FTQ100 Datasheet(HTML) 8 Page - Actel Corporation |
8 / 49 page eX Family FPGAs 1- 4 v4.3 Clock Resources eX’s high-drive routing structure provides three clock networks. The first clock, called HCLK, is hardwired from the HCLK buffer to the clock select MUX in each R-Cell. HCLK cannot be connected to combinational logic. This provides a fast propagation path for the clock signal, enabling the 3.9 ns clock-to-out (pad-to-pad) performance of the eX devices. The hard-wired clock is tuned to provide a clock skew of less than 0.1 ns worst case. If not used, the HCLK pin must be tied LOW or HIGH and must not be left floating. Figure 1-5 describes the clock circuit used for the constant load HCLK. HCLK does not function until the fourth clock cycle each time the device is powered up to prevent false output levels due to any possible slow power-on-reset signal and fast start-up clock circuit. To activate HCLK from the first cycle, the TRST pin must be reserved in the Design software and the pin must be tied to GND on the board. (See the "TRST, I/O Boundary Scan Reset Pin" on page 1- 26). The remaining two clocks (CLKA, CLKB) are global routed clock networks that can be sourced from external pins or from internal logic signals (via the CLKINT routed clock buffer) within the eX device. CLKA and CLKB may be connected to sequential cells or to combinational logic. If CLKA or CLKB is sourced from internal logic signals, the external clock pin cannot be used for any other input and must be tied LOW or HIGH and must not float. Figure 1-6 describes the CLKA and CLKB circuit used in eX devices. Table 1-1 describes the possible connections of the routed clock networks, CLKA and CLKB. Unused clock pins must not be left floating and must be tied to HIGH or LOW. Figure 1-5 • eX HCLK Clock Pad Constant Load Clock Network HCLKBUF Figure 1-6 • eX Routed Clock Buffer Clock Network From Internal Logic CLKBUF CLKBUFI CLKINT CLKINTI Table 1-1 • Connections of Routed Clock Networks, CLKA and CLKB Module Pins C-Cell A0, A1, B0 and B1 R-Cell CLKA, CLKB, S0, S1, PSET, and CLR I/O-Cell EN |
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