Delta39K™ ISR™
CPLD Family
Programmable Bus Hold
For example, a system that operates on a 32-bit data path that
runs at 40 MHz can be implemented with 16-bit circuitry that
runs internally at 80 MHz. PLLs can also be used to take
advantage of the positioning of the internally generated clock
edges to shift performance towards improved setup, hold or
clock-to-out times.
On each I/O pin, user-programmable-bus-hold is included.
Bus-hold, which is an improved version of the popular internal
pull-up resistor, is a weak latch connected to the pin that does
not degrade the device’s performance. As a latch, bus-hold
maintains the last state of a pin when the pin is placed in a
high-impedance state, thus reducing system noise in bus-
interface applications. Bus-hold additionally allows unused
device pins to remain unconnected on the board, which is
particularly useful during prototyping as designers can route
new signals to the device without cutting trace connections to
VCC or GND. For more information, see the application note
titled “Understanding Bus-Hold–A Feature of Cypress
CPLDs.”
There are several frequency multiply (X1, X2, X3, X4, X5, X6,
X8, X16) and divide (/1, /2, /3, /4, /5, /6, /8, /16) options
available to create a wide range of clock frequencies from a
single clock input (GCLK[0]). For increased flexibility, there are
seven phase shifting options which allow clock skew/deskew
by 45°, 90°, 135°, 180°, 225°, 270°, or 315°.
The Spread Aware feature refers to the ability of the PLL to
track a spread-spectrum input clock such that its spread is
seen on the output clock with the PLL staying locked. The total
amount of spread on the input clock should be limited to 0.6%
of the fundamental frequency. Spread Aware feature is
supported only with X1, X2, and X4 multiply options.
Clocks
Delta39K has four dedicated clock input pins (GCLK[3:0]) to
accept system clocks. One of these clocks (GCLK[0]) may be
selected to drive an on-chip phase-locked loop (PLL) for
frequency modulation (see Figure 9 for details).
The Voltage Controlled Oscillator (VCO), the core of the
Delta39K PLL is designed to operate within the frequency
range of 100 MHz to 266 MHz. Hence, the multiply option
combined with input (GCLK[0]) frequency should be selected
such that this VCO operating frequency requirement is met.
This is demonstrated in Table 4 (columns 1, 2, and 3).
The global clock tree for a Delta39K device can be driven by
a combination of the dedicated clock pins and/or the PLL-
derived clocks. The global clock tree consists of four global
clocks that go to every macrocell, memory block, and I/O cell.
Clock Tree Distribution
Another feature of this PLL is the ability to drive the output
clock (INTCLK) off the Delta39K chip to clock other devices on
the board, as shown in Figure 9 above. This off-chip clock is
half the frequency of the output clock as it has to go through a
register (I/O register or a macrocell register).
The global clock tree performs two primary functions. First, the
clock tree generates the four global clocks by multiplexing four
dedicated clocks from the package pins and four PLL driven
clocks. Second, the clock tree distributes the four global clocks
to every cluster, channel memory, and I/O block on the die.
The global clock tree is designed such that the clock skew is
minimized while maintaining an acceptable clock delay.
This PLL can also be used for board de-skewing purpose by
driving a PLL output clock off-chip, routing it to the other
devices on the board and feeding it back to the PLL’s external
feedback input (GCLK[1]). When this feature is used, only
limited multiply, divide and phase shift options can be used.
Table 4 describes the valid multiply and divide options that can
be used without external feedback. Table 5 describes the valid
multiply and divide options that can be used with an external
feedback.
Spread Aware PLL
Each device in the Delta39K family features an on-chip PLL
designed using Spread Aware technology for low EMI applica-
tions. In general, PLLs are used to implement time-division-
multiplex circuits to achieve higher performance with fewer
device resources.
off-chip signal (external feedback)
INTCLK0, INTCLK1, INTCLK2, INTCLK3
Any Register (TFF)
Send a global clock off
chip
GCLK1
Normal I/O signal path
Lock Detect/IO pin
C
Clock Tree
Delay
Phase selection
Divide
¸1-6,8,16
2
C
INTCLK0
GCLK0
fb
fb
Lock
2
Phase selection
C
Divide
¸ 1-6,8,16
Clk
00
0
Clk 45
INTCLK1
GCLK1
Clk
0
2
Phase selection
GCLK0
90
Clk 135
Source
Clock
C
0
Divide
¸1-6,8,16
0
Clk 180
Clk
INTCLK2
0
225
Clk
GCLK2
0
270
Clk
2
PLL
X1, X2, X3, X4, 5X,
0
315
C
Phase selection
X6, X8, X16
Divide
¸1-6,8,16
INTCLK3
GCLK3
2
C
Figure 9. Block Diagram of Spread Aware PLL
Document #: 38-03039 Rev. *H
Page 11 of 86
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