Rainbow Electronics ATF1502ASV - Manual (Page 7)

7
ATF1502ASV
1615G–PLD–09/02
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 ATF1502ASV 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 application 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
ATF1502ASV 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 ATF1502ASV is designed with a power-up reset, a feature critical for state machine
initialization. At a point delayed slightly from V
CC
crossing V
RST
, all registers will be ini-
tialized, and the state of each output will depend on the polarity of its buffer. However,
due to the asynchronous 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 ATF1502ASV has two options for the hysteresis about the reset level, V
RST
, Small
and Large. To ensure a robust operating environment in applications where the device
is operated near 3.0V, Atmel recommends that during the fitting process users configure
the device with the Power-up Reset hysteresis set to Large. For conversions, Atmel
POF2JED users should include the flag “-power_reset” on the command line after “file-
name.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 micro-
amps as well.
Security Fuse Usage
A single fuse is provided to prevent unauthorized copying of the ATF1502ASV fuse pat-
terns. Once programmed, fuse verify is inhibited. However, the 16-bit User Signature
remains accessible.
Programming
ATF1502ASV devices are in-system programmable (ISP) devices utilizing the 4-pin
JTAG protocol. This capability eliminates package handling normally required for pro-
gramming and facilitates rapid design iterations and field changes.
Atmel provides ISP hardware and software to allow programming of the ATF1502ASV
via the PC. ISP is performed by using either a download cable, a comparable board
tester or a simple microprocessor interface.