General Description
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R ev isio n 1 8
Global Resources
Each family member has three types of global signals available to the designer: HCLK, CLK, and
GCLR/GPSET. There are four hardwired clocks (HCLK) per device that can directly drive the clock input
of each R-cell. Each of the four routed clocks (CLK) can drive the clock, clear, preset, or enable pin of an
Global clear (GCLR) and global preset (GPSET) drive the clear and preset inputs of each R-cell as well
as each I/O Register on a chip-wide basis at power-up.
Each HCLK and CLK has an associated analog PLL (a total of eight per chip). Each embedded PLL can
be used for clock delay minimization, clock delay adjustment, or clock frequency synthesis. The PLL is
capable of operating with input frequencies ranging from 14 MHz to 200 MHz and can generate output
frequencies between 20 MHz and 1 GHz. The clock can be either divided or multiplied by factors ranging
from 1 to 64. Additionally, multiply and divide settings can be used in any combination as long as the
resulting clock frequency is between 20 MHz and 1 GHz. Adjacent PLLs can be cascaded to create
complex frequency combinations.
The PLL can be used to introduce either a positive or a negative clock delay of up to 3.75 ns in 250 ps
increments. The reference clock required to drive the PLL can be derived from three sources: external
input pad (either single-ended or differential), internal logic, or the output of an adjacent PLL.
Low Power (LP) Mode
The AX architecture was created for high-performance designs but also includes a low power mode
(activated via the LP pin). When the low power mode is activated, I/O banks can be disabled (inputs
disabled, outputs tristated), and PLLs can be placed in a power-down mode. All internal register states
are maintained in this mode. Furthermore, individual I/O banks can be configured to opt out of the LP
mode, thereby giving the designer access to critical signals while the rest of the chip is in low power
mode.
The power can be further reduced by providing an external voltage source (VPUMP) to the device to
Figure 1-8
AX Routing Structures