14
Lucent Technologies Inc.
Preliminary Data Sheet, Rev. 1
ORCA Series 3 FPGAs
September 1998
Programmable Logic Cells (continued)
The ripple mode can be used in one of four submodes.
The first of these is adder-subtractor submode. In this
submode, each LUT generates three separate outputs.
One of the three outputs selects whether the carry-in is
to be propagated to the carry-out of the current LUT or if
the carry-out needs to be generated. If the carry-out
needs to be generated, this is provided by the second
LUT output. The result of this selection is placed on the
carry-out signal, which is connected to the next LUT
carry-in or the COUT/FCOUT signal, if it is the last LUT
(K7/K3). Both of these outputs can be any equation cre-
ated from KZ[1] and KZ[0], but in this case they have
been set to the propagate and generate functions.
The third LUT output creates the result bit for each LUT
output connected to F[7:0]/F[3:0]. If an adder/subtractor is
needed, the control signal to select addition or subtrac-
tion is input on ASWE, with a logic 0 indicating subtrac-
tion and a logic 1 indicating addition. The result bit is
created in one-half of the LUT from a single bit from
each input bus KZ[1:0], along with the ripple input bit.
The second submode is the counter submode (see
Figure 7). The present count, which may be initialized
via the PFU DIN inputs to the latches/FFs, is supplied to
input KZ[0], and then output F[7:0]/F[3:0] will either be
incremented by one for an up counter or decremented
by one for a down counter. If an up/down counter is
needed, the control signal to select the direction (up or
down) is input on ASWE with a logic 1 indicating an up
counter and a logic 0 indicating a down counter. Gener-
ally, the latches/FFs in the same PFU are used to hold
the present count value.
Figure 7. Counter Submode
5-5756(F)
F7
K7[0]
K7
D
Q
C
DQ
Q7
REGCOUT
COUT
F6
K6[0]
K6
D
Q
Q6
F4
K4[0]
K4
D
Q
Q4
F3
K3[0]
K3
D
Q
Q3
F2
K2[0]
K2
D
Q
Q2
F1
K1[0]
K1
D
Q
Q1
F5
K5[0]
K5
D
Q
Q5
F0
K0[0]
K0
D
Q
Q0
CIN/FCIN
FCOUT