PALCE26V12 Datasheet, PDF (4/21 Pages) Advanced Micro Devices – 28-Pin EE CMOS Versatile PAL Device

FUNCTIONAL DESCRIPTION
The PALCE26V12 has fourteen dedicated input lines,
two of which can be used as clock inputs. Unused inputs
should be tied directly to ground or VCC. Buffers for
device inputs and feedbacks have both true and
complementary outputs to provide user-selectable
signal polarity. The inputs drive a programmable AND
logic array, which feeds a fixed OR logic array.
The OR gates feed the twelve I/O macrocells (see
Figure 1). The macrocell allows one of eight potential
output configurations; registered or combinatorial, ac-
tive high or active low, with register or I/O pin feedback
(see Figure 2). In addition, registered configurations can
be clocked by either of the two clock inputs.
The configuration choice is made according to the
user’s design specification and corresponding program-
ming of the configuration bits S0–S3 (see Table 1).
Multiplexer controls initially float to VCC (1) through a
programmable cell, selecting the “1” path through the
multiplexer. Programming the cell connects the control
line to GND (0), selecting the “0” path.
Table 1. Macrocell Configuration Table
S3 S1 S0 Output Configuration
100
Registered Output and Feedback,
Active Low
101
Registered Output and Feedback,
Active High
1 1 0 Combinatorial I/O, Active Low
1 1 1 Combinatorial I/O, Active High
0 0 0 Registered I/O, Active Low
0 0 1 Registered I/O, Active High
010
Combinatorial Output, Registered
Feedback, Active Low
011
Combinatorial Output, Registered
Feedback, Active High
1 = Unprogrammed EE bit
0 = Programmed EE bit
S2 Clock Input
1 CLK1/I0
0 CLK2/I3
AMD
OE
P1
Pn
n = 8,8,10,12,14,16
AR CLK ₁
AR
DQ
1
0
Q
SP
CLK2 ^S2
0
SP
1
10
11
00
01
S0
S1
S3*
* When S ₃ = 1 (unprogrammed) the feedback is selected by S1.
When S3 = 0 (programmed), the feedback is the opposite of
that selected by S1.
16072E-4
Figure 1. PALCE26V12 Macrocell
Registered or Combinatorial
Each macrocell of the PALCE26V12 includes a D-type
flip-flop for data storage and synchronization. The
flip-flop is loaded on the LOW-to-HIGH edge of the
selected clock input. Any macrocell can be configured
as combinatorial by selecting a multiplexer path that
bypasses the flip-flop. Bypass is controlled by bit S1.
Programmable Clock
The clock input for any flip-flop can be selected to be
from either pin 1 or pin 4. A 2:1 multiplexer controlled by
bit S2 determines the clock input.
Programmable Feedback
A 2:1 multiplexer allows the user to determine whether
the macrocell feedback comes from the flip-flop or
from the I/O pin, independent of whether the output is
registered or combinatorial. Thus, registered outputs
may have internal register feedback for higher speed
(fMAX internal), or I/O feedback for use of the pin as a
direct input (fMAX external). Combinatorial outputs may
have I/O feedback, either for use of the signal in other
equations or for use as another direct input, or register
feedback.
PALCE26V12 Family
2–309