4

ATC25 Summary

1306DS–CBIC–09/02

Input/Output Pad Cell

Libraries

IO25lib and IO33lib

The Atmel Input/Output Cell Library, IO25lib, contains a comprehensive list of input, out-

put, bidirectional and tristate cells. The ATC25 (2.5V) cell library includes a special set

of I/O cells, IO33lib, for interfacing with external 3V devices.

Voltage Levels

The IO25lib library is made up exclusively of low-voltage chip interface circuits powered

by a voltage in the range of 2.25V to 2.75V. The library is compatible with the SClib 2.5-

volt standard cells library.

Power and Ground Pads

Designers are strongly encouraged to provide three kinds of power pairs for the IO25lib

library. These are “AC”, “DC” and core power pairs. AC power is used by the I/O to

switch its output from one state to the other. This switching generates noise in the AC

power buses on the chip. DC power is used by the I/O to maintain its output in a steady

state. The best noise performance is achieved when the DC power buses on the chip

are free of noise; designers are encouraged to use separate power pairs for AC and DC

power to prevent most of the noise in the AC power buses from reaching the DC power

buses. The same power pairs can be used to supply both DC power to the I/Os and

power to the core without affecting noise performance.

Table 6. VSS Power Pad Combinations

Core

Switching I/O

Quiet I/O

Library Cell

Name

Signal Name

Vssi

VssAC

VssDC

•

pv25i00

VSS

•

pv25a00

VSS

•

pv25d00

VSS

••

pv25e00

VSS

••

pv25b00

VSS

•••

pv25f00

VSS

Table 7. VDD Power Pad Combinations

Core

Switching I/O

Quiet I/O

Library Cell

Name

Signal Name

Vddi

VddAC

VddDC

•

pv25i25

VDD

•

pv25a25

VDD

•

pv25d25

VDD

••

pv25e25

VDD

••

pv25b25

VDD

•••

pv25f25

VDD