Rainbow Electronics ATF1500AL - Manual (Page 11)

ATF1500A(L)
11
Power Up Reset
The ATF1500A’s registers are designed to reset during
power up. At a point delayed slightly from V
CC
crossing
V
RST
, all registers will be reset to the low state. As a result,
the registered output state will always be low on power-up.
This feature is critical for state machine initialization. How-
ever, due to the asynchronous nature of reset and the
uncertainty of how V
CC
actually rises in the system, the fol-
lowing conditions are required:
1. The V
CC
rise must be monotonic, from below 0.7 volt,
2. After reset occurs, all input and feedback setup times
must be met before driving the clock signal high, and
3. Signals from which clocks are derived must remain sta-
ble during t
PR
.
Power Down Mode
The ATF1500A includes an optional pin controlled power
down feature. When this mode is enabled, the PD pin acts
as the power down pin. When the PD pin is high, the device
supply current is reduced to less than 10 mA. During power
down, all output data and internal logic states are latched
and held. Therefore, all registered and combinatorial output
data remain valid. Any outputs which were in a HI-Z state at
the onset of power down will remain at HI-Z. During power
down, all input signals except the power down pin are
blocked. Input and I/O hold latches remain active to insure
that pins do not float to indeterminate levels, further reduc-
ing system power. The power down pin feature is enabled
in the logic design file. Designs using the power down pin
may not use the PD pin logic array input. However, all other
PD pin macrocell resources may still be used, including the
buried feedback and foldback product term array inputs.
Register Preload
The ATF1500A’s registers are provided with circuitry to
allow loading of each register with either a high or a low.
This feature will simplify testing since any state can be
forced into the registers to control test sequencing. A
JEDEC file with preload is generated when a source file
with preload vectors is compiled. Once downloaded, the
JEDEC file preload sequence will be done automatically
when vectors are run by any approved programmers. The
preload mode is enabled by raising an input pin to a high
voltage level. Contact Atmel PLD Applications for PRE-
LOAD pin assignments, timing and voltage requirements.
Output Slew Rate Control
Each ATF1500A macrocell contains a configuration bit for
each I/O to control its output slew rate. This allows selected
data paths to operate at maximum throughput while reduc-
ing system noise from outputs that are not speed-critical.
Outputs default to slow edges, and may be individually set
to fast in the design file. Output transition times for outputs
configured as “slow” have a t
SSO
delay adder.
Security Fuse Usage
A single fuse is provided to prevent unauthorized copying
of the ATF1500A fuse patterns. Once programmed, fuse
verify and preload are prohibited. However, the 160-bit
User Signature remains accessible.
The security fuse should be programmed last, as its effect
is immediate.
Parameter Description Typ Max Units
t
PR
Power-Up
Reset Time
2 10
µ
s
V
RST
Power-Up
Reset
Voltage
3.8 4.5 V