Specifications GAL16V8
Switching Test Conditions (Continued)
GAL16V8D-3 Output Load Conditions (see figure at right)
+1.45V
Test Condition
R1
CL
TEST POINT
A
B
50Ω
50Ω
50Ω
50Ω
50Ω
35pF
35pF
35pF
35pF
35pF
R1
High Z to Active High at 1.9V
High Z to Active Low at 1.0V
Active High to High Z at 1.9V
Active Low to High Z at 1.0V
FROM OUTPUT (O/Q)
UNDER TEST
Z0 = 50Ω, CL = 35pF*
C
*CL includes test fixture and probe capacitance.
Electronic Signature
Output Register Preload
An electronic signature is provided in every GAL16V8 device. It
contains 64 bits of reprogrammable memory that can contain user
defined data. Some uses include user ID codes, revision numbers,
or inventory control. The signature data is always available to the
user independent of the state of the security cell.
When testing state machine designs, all possible states and state
transitions must be verified in the design, not just those required
in the normal machine operations. This is because, in system
operation, certain events occur that may throw the logic into an
illegal state (power-up, line voltage glitches, brown-outs, etc.). To
test a design for proper treatment of these conditions, a way must
be provided to break the feedback paths, and force any desired (i.e.,
illegal) state into the registers. Then the machine can be sequenced
and the outputs tested for correct next state conditions.
NOTE: The electronic signature is included in checksum calcula-
tions. Changing the electronic signature will alter the checksum.
Security Cell
GAL16V8 devices include circuitry that allows each registered
output to be synchronously set either high or low. Thus, any present
state condition can be forced for test sequencing. If necessary,
approved GAL programmers capable of executing text vectors
perform output register preload automatically.
A security cell is provided in the GAL16V8 devices to prevent un-
authorized copying of the array patterns. Once programmed, this
cell prevents further read access to the functional bits in the device.
This cell can only be erased by re-programming the device, so the
original configuration can never be examined once this cell is pro-
grammed. The Electronic Signature is always available to the user,
regardless of the state of this control cell.
Input Buffers
GAL16V8 devices are designed with TTL level compatible input
buffers. These buffers have a characteristically high impedance,
and present a much lighter load to the driving logic than bipolar TTL
devices.
Latch-Up Protection
GAL16V8 devices are designed with an on-board charge pump
to negatively bias the substrate. The negative bias minimizes the
potential of latch-up caused by negative input undershoots. Ad-
ditionally, outputs are designed with n-channel pull-ups instead of
the traditional p-channel pull-ups in order to eliminate latch-up due
to output overshoots.
The GAL16V8 input and I/O pins have built-in active pull-ups. As
a result, unused inputs and I/O's will float to a TTL "high" (logical
"1"). Lattice Semiconductor recommends that all unused inputs
and tri-stated I/O pins be connected to another active input, VCC
,
or Ground. Doing this will tend to improve noise immunity and re-
duce ICC for the device.
Device Programming
GAL devices are programmed using a Lattice Semiconductor-
approved Logic Programmer, available from a number of manu-
facturers. Complete programming of the device takes only a few
seconds. Erasing of the device is transparent to the user, and is
done automatically as part of the programming cycle.
Typical Input Pull-up Characteristic
0
- 2 0
- 4 0
- 6 0
0
1 . 0
2 . 0
3 . 0
4 . 0
5 . 0
Input Voltage (Volts)
15
LATTICE [ LATTICE SEMICONDUCTOR ]
