OR2C04A datasheet(26/192 Pages) ETC

26 / 192 page

Lucent Technologies Inc.

Data Sheet

ORCA Series 2 FPGAs

June 1999

Programmable Input/Output Cells

(continued)

A. Simplified Diagram of OR2CxxA Programmable

I/O Cell (PIC)

B. Simplified Diagram of OR2TxxA/OR2TxxB

Programmable I/O Cell (PIC)

Figure 24. Simplified Diagrams

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 current to 24 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 PCB, and loads and is best determined

with a circuit simulation.

Outputs can be inverted, and 3-state control signals

can be active-high or active-low. An open-drain output

may be obtained by using the same signal for driving

the output and 3-state signal nets so that the buffer out-

put is enabled only by a low. At powerup, the output

drivers are in slewlim mode, and the input buffers are

configured as TTL-level compatible with a pull-up. If an

output is not to be driven in the selected configuration

mode, it is 3-stated.

5 V Tolerant I/O (OR2TxxA)

The I/O on the OR2TxxA series devices allow intercon-

nection to both 3.3 V and 5 V device (selectable on a

per-pin basis) by way of special VDD5 pins that have

been added to the OR2TxxA devices. If any I/O on the

OR2TxxA device interfaces to a 5 V input, then all of

the VDD5 pins must be connected to the 5 V supply. If

no pins on the device interface to a 5 V signal, then the

VDD5 pins must be connected to the 3.3 V supply.

If the VDD5 pins are disconnected (i.e., they are float-

ing), the device will not be damaged; however, the

device may not operate properly until VDD5 is returned

to a proper voltage level. If the VDD5 pins are then

shorted to ground, a large current flow will develop, and

the device may be damaged.

PULL-UP

VDD

DELAY

TTL/CMOS

PAD

SLEW RATE

POLARITY

DOUT/OUT

PULL-DOWN

dintb, dinlr

POLARITY

TRI

5-4591(F)

PULL-UP

VDD

DELAY

PAD

SLEW RATE

POLARITY

DOUT/OUT

PULL-DOWN

dintb, dinlr

POLARITY

TRI

5-4591.T(F)

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