Specifications GAL16VP8
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.
Electronic Signature
An electronic signature word is provided in every GAL16VP8 de-
vice. It contains 64 bits of reprogrammable memory that can contain
user defined data. Some uses include user ID codes, revision num-
bers, or inventory control. The signature data is always available
to the user independent of the state of the security cell.
The GAL16VP8 device includes 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.
NOTE: The electronic signature is included in checksum calcula-
tions. Changing the electronic signature will alter the checksum.
If necessary, approved GAL programmers capable of executing test
vectors can perform output register preload automatically.
Security Cell
The security cell is provided on all GAL16VP8 devices to prevent
unauthorized copying of the array patterns. Once programmed,
Input Buffers
the circuitry enabling array is disabled, preventing further program- GAL16VP8 devices are designed with TTL level compatible input
ming or verification of the array. The cell can only be erased by re- buffers. These buffers have a characteristically high impedance,
programming the device, so the original configuration can never and present a much lighter load to the driving logic than bipolar TTL
be examined once this cell is programmed. Signature data is al- devices.
ways available to the user.
GAL16VP8 input buffers have active pull-ups within their input
structure. As a result, unused inputs and I/O's will float to a TTL
"high" (logical "1"). Lattice Semiconductor recommends that all un-
Latch-Up
used inputs and tri-stated I/O pins for both devices be connected
to another active input, VCC, or GND. Doing this will tend to improve
noise immunity and reduce ICC for the device.
GAL16VP8 devices are designed with an on-board charge pump
to negatively bias the substrate. The negative bias is of sufficient
magnitude to prevent input undershoots from causing the circuitry
to latch. Additionally, outputs are designed with n-channel pull-ups
instead of the traditional p-channel pull-ups to eliminate any pos-
sibility of SCR induced latching.
Typical Input Pull-up Characteristic
0
Bulk Erase Mode
- 2 0
During a programming cycle, a clear function performs a bulk erase
of the array and the architecture word. In addition, the electronic
signature word and the security cell are erased. This mode resets
a previously configured device back to its original state, which is
all JEDEC ones.
- 4 0
- 6 0
0
1 . 0
2 . 0
3 . 0
4 . 0
5 . 0
Input Voltage (Volts)
Scmitt Trigger Inputs
One of the enhancements of the GAL16VP8 for bus interface logic
implementation is input hysteresis. The threshold of the positive
going edge is 1.5V, while the threshold of the negative going edge
is 1.3V. This provides a typical hysteresis of 200mV between
positive and negative transitions of the inputs.
Programmable Open-Drain Outputs
In addition to the standard GAL16V8 type configuration, the out-
puts of the GAL16VP8 are individually programmable either as a
standard totempole output or an open-drain output. The totempole
output drives the specified VOH and VOL levels whereas the open-
drain output drives only the specified VOL. The VOH level on the
open-drain output depends on the external loading and pull-up. This
output configuration is controlled by theAC2 fuse. When AC2 cell
is erased (JEDEC "1") the output is configured as a totempole out-
put and when AC2 cell is programmed (JEDEC "0") the output is
configured as an open-drain. The default configuration when the
device is in bulk erased state is totempole configuration. TheAC2
fuses associated with each of the outputs is included in all of the
logic diagrams.
High Drive Outputs
All eight outputs of the GAL16VP8 are capable of driving 64 mA
loads when driving low and 32 mA loads when driving high. Near
symmetrical high and low output drive capability provides small
skews between high-to-low and low-to-high output transitions.
Output Register Preload
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
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LATTICE [ LATTICE SEMICONDUCTOR ]
