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Quantum38K ISR
CPLD Family
Document #: 38-03043 Rev. *G
Page 6 of 45
implement adders, subtractors, magnitude comparators,
parity tree, or even generic XOR logic. The output of the
macrocell is either registered or combinatorial.
Carry Chain Logic
The Quantum38K macrocell features carry chain logic which
is used for fast and efficient implementation of arithmetic
operations. The carry logic connects macrocells in up to four
logic blocks for a total of 64 macrocells. Effective data path
operations are implemented through the use of carry-in arith-
metic, which drives through the circuit quickly. Figure 4 shows
that the carry chain logic within the macrocell consists of two
product terms (CPT0 and CPT1) from the PTA and an input
carry-in for carry logic. The inputs to the carry chain mux are
connected directly to the product terms in the PTA. The output
of the carry chain mux generates the carry-out for the next
macrocell in the logic block as well as the local carry input that
is connected to an input of the XOR input mux. Carry-in and a
configuration bit are inputs to an AND gate. This AND gate
provides a method of segmenting the carry chain in any
macrocell in the logic block.
Macrocell Clocks
Clocking of the register is highly flexible. Four global
synchronous clocks (GCLK[3:0]) and a Product Term clock
(PTCLK)
are
available
at
each
macrocell
register.
Furthermore, a clock polarity mux within each macrocell
allows the register to be clocked on the rising or the falling
edge (see macrocell diagram in Figure 4).
PRESET/RESET Configurations
The macrocell register can be asynchronously preset and
reset using the PRESET and RESET mux. Both signals are
active high and can be controlled by either of two Preset/Reset
product terms (PRC[1:0] in Figure 4) or GND. In situations
where the PRESET and RESET are active at the same time,
RESET takes priority over PRESET.
Figure 4. Quantum38K Macrocell
D
Q
PSET
RES
GCLK[3:0]
PTCLK
FROM PTM
CPT0
CPT1
P
R
C
[1:0]
0
1
0
1
To PIM
C
Carry Out
(to macrocell n+1)
Carry In
(from macrocell n-1)
Up To 16 PTs
PRESET
Mux
Clock
Polarity
Mux
RESET
Mux
Clock Mux
Carry Chain
Mux
XOR Input
Mux
Output Mux
Q
C
3
2
3
C