Specifications GAL26CV12
Electronic Signature
Output Register Preload
An electronic signature is provided in every GAL26CV12 device. When testing state machine designs, all possible states and state
It contains 64 bits of reprogrammable memory that can contain transitions must be verified in the design, not just those required
user-defined data. Some uses include user ID codes, revision in normal machine operation. This is because certain events may
numbers, or inventory control. The signature data is always avail- occur during system operation that throw the logic into an illegal
able to the user independent of the state of the security cell.
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.
Security Cell
A security cell is provided in every GAL26CV12 device to prevent
unauthorized 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 de-
vice, so the original configuration can never be examined once this
cell is programmed. The Electronic Signature is always available
to the user, regardless of the state of this control cell.
The GAL26CV12 device includes circuitry that allows each regis-
tered output to be synchronously set either high or low. Thus, any
present state condition can be forced for test sequencing. If nec-
essary, approved GAL programmers capable of executing test
vectors perform output register preload automatically.
Input Buffers
Latch-Up Protection
GAL26CV12 devices are designed with TTL level compatible in-
put buffers. These buffers have a characteristically high impedance,
and present a much lighter load to the driving logic than bipolar TTL
logic.
GAL26CV12 devices are designed with an on-board charge pump
to negatively bias the substrate. The negative bias minimizes the
potential for 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 input and I/O pins also have built-in active pull-ups. As a result,
floating inputs will float to a TTL high (logic 1). However, Lattice
Semiconductor recommends that all unused inputs and tri-stated
I/O pins be connected to an adjacent active input, Vcc, or ground.
Doing so will tend to improve noise immunity and reduce Icc for the
Device Programming
GAL devices are programmed using a Lattice Semiconductor-
approved Logic Programmer, available from a number of manu-
facturers (see the the GAL Development Tools section). 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.
device.
Typical Input Current
0
- 2 0
- 4 0
- 6 0
0
1 . 0
2 . 0
3 . 0
4 . 0
5 . 0
Input Voltage (Volts)
12
LATTICE [ LATTICE SEMICONDUCTOR ]
