Rainbow Electronics ATF1502ASL - Manual (Page 7)

7
ATF1502AS(L)
0995J–PLD–09/02
All pin transitions are ignored until the PD pin is brought low. When the power-down feature is
enabled, the PD1 or PD2 pin cannot be used as a logic input or output. However, the pin’s
macrocell may still be used to generate buried foldback and cascade logic signals.
All power-down AC characteristic parameters are computed from external input or I/O pins,
with reduced-power bit turned on. For macrocells in reduced-power mode (reduced-power bit
turned on), the reduced-power adder, t
RPA
, must be added to the AC parameters, which
include the data paths t
LAD
, t
LAC
, t
IC
, t
ACL
, t
ACH
and t
SEXP
.
The ATF1502AS macrocell also has an option whereby the power can be reduced on a per-
macrocell basis. By enabling this power-down option, macrocells that are not used in an appli-
cation can be turned down, thereby reducing the overall power consumption of the device.
Each output also has individual slew rate control. This may be used to reduce system noise by
slowing down outputs that do not need to operate at maximum speed. Outputs default to slow
switching, and may be specified as fast switching in the design file.
Design
Software
Support
ATF1502AS designs are supported by several third-party tools. Automated fitters allow logic
synthesis using a variety of high-level description languages and formats.
Power-up Reset
The ATF1502AS is designed with a power-up reset, a feature critical for state machine initial-
ization. At a point delayed slightly from V
CC
crossing V
RST
, all registers will be initialized, and
the state of each output will depend on the polarity of its buffer. However, due to the asynchro-
nous nature of reset and uncertainty of how V
CC
actually rises in the system, the following
conditions are required:
1. The V
CC
rise must be monotonic,
2. After reset occurs, all input and feedback setup times must be met before driving the
clock pin high, and,
3. The clock must remain stable during T
D
.
The ATF1502AS has two options for the hysteresis about the reset level, V
RST
, Small and
Large. During the fitting process users may configure the device with the Power-up Reset hys-
teresis set to Large or Small. Atmel POF2JED users may select the Large option by including
the flag “-power_reset” on the command line after “filename.POF”. To allow the registers to be
properly reinitialized with the Large hysteresis option selected, the following condition is
added:
4. If V
CC
falls below 2.0V, it must shut off completely before the device is turned on again.
When the Large hysteresis option is active, I
CC
is reduced by several hundred microamps as
well.
Security Fuse
Usage
A single fuse is provided to prevent unauthorized copying of the ATF1502AS fuse patterns.
Once programmed, fuse verify is inhibited. However, the 16-bit User Signature remains
accessible.
Programming
ATF1502AS devices are in-system programmable (ISP) devices utilizing the 4-pin JTAG pro-
tocol. This capability eliminates package handling normally required for programming and
facilitates rapid design iterations and field changes.