OR3T125-5BA352 AGERE [Agere Systems], OR3T125-5BA352 Datasheet - Page 41

• Manufacturer Part Number: OR3T125-5BA352
• Description: 3C and 3T Field-Programmable Gate Arrays
• Manufacturer: AGERE [Agere Systems]

Data Sheet
June 1999
Programmable Input/Output Cells
(continued)
Outputs
The PIC’s output drivers have programmable drive
capability and slew rates. Three propagation delays
(fast, slewlim, sinklim) are available on output drivers.
The sinklim mode has the longest propagation delay
and is used to minimize system noise and minimize
power consumption. The fast and slewlim modes allow
critical timing to be met.
The drive current is 12 mA sink/6 mA source for the
slewlim and fast output speed selections and
6 mA sink/3 mA source for the sinklim output. Two adja-
cent outputs can be interconnected to increase the out-
put sink/source current to 24 mA/12 mA.
All outputs that are not speed critical should be config-
ured as sinklim to minimize power and noise. The num-
ber of outputs that switch simultaneously in the same
direction should be limited to minimize ground bounce.
To minimize ground bounce problems, locate heavily
loaded output buffers near the ground pads. Ground
bounce is generally a function of the driving circuits,
traces on the printed-circuit board, and loads and is
best determined with a circuit simulation.
At powerup, the output drivers are in slewlim mode,
and the input buffers are configured as TTL-level com-
patible (CMOS for OR3Txxx) with a pull-up. If an output
is not to be driven in the selected configuration mode, it
is 3-stated.
The output buffer signal can be inverted, and the
3-state control signal can be made active-high, active-
low, or always enabled. In addition, this 3-state signal
can be registered or nonregistered. Additionally, there
is a fast, open-drain output option that directly connects
the output signal to the 3-state control, allowing the out-
put buffer to either drive to a logic 0 or 3-state, but
never to drive to a logic 1. Because there is no explicit
route required to create the open-drain output, its
response is very fast. Like the input side of the PIO,
there are two output connections from PIC routing to
the output side of the PIO, OUT1, and OUT2. These
connections provide for flexible routing and can be
used in data manipulation in the PIO as described in
subsequent paragraphs.
Lucent Technologies Inc.
An FF has been added to the output path of the PIO.
The register has a local set/reset and clock enable. The
LSR has the option to be synchronous or asynchro-
nous and have priority set as clock enable over LSR or
LSR over clock enable. Clocking to the output FF can
come from either the system clock or the ExpressCLK
associated with the PIC. The input to the FF can come
from either OUT1 or OUT2, or it can be tied to V
GND. Additionally, the input to the FF can be inverted.
Output Multiplexing
The Series 3 PIO output FF can be combined with the
new PIO logic block to perform output data multiplexing
with no PLC resources required. The PIO logic block
has three multiplexing modes: OUT1OUTREG,
OUT2OUTREG, and OUT1OUT2. OUT1OUTREG and
OUT2OUTREG are equivalent except that either OUT1
or OUT2 is MUXed with the FF, where the FF data is
output on the clock phase after the active edge. The
simplest multiplexing mode is OUT1OUT2. In this
mode, the signal at OUT1 is output to the pad while the
clock is low, and the signal on OUT2 is output to the
pad when the clock is high. Figure 25 shows a simple
schematic of a PIO in OUT1OUT2 mode and a general
timing diagram for multiplexing an address and data
signal.
Often an address will be used to generate or read a
data sample from memory with the goal of multiplexing
the data onto a single line. In this case, the address
often precedes the data by one clock cycle.
OUT1OUTREG and OUT2OUTREG modes of the PIO
logic can be used to address this situation.
Because OUT1OUTREG mode is equivalent to
OUT2OUTREG, only OUT2OUTREG mode is
described here. Figure 26 shows a simple PIO sche-
matic in OUT2OUTREG mode and general timing for
multiplexing data with a leading address. The address
signal on OUT1 is registered in the PIO FF. This delays
the address so that it aligns with the data signal. The
PIO logic block then sends the OUTREG signal
(address) to the pad when the clock is high and the
OUT2 signal (data) to the pad when the clock is low,
resulting in an aligned, multiplexed signal.
ORCA Series 3C and 3T FPGAs
DD
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