CDPCLK4 datasheet(249/274 Pages) ALTERA

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Chapter 10: Hot-Socketing and Power-On Reset in the Cyclone III Device Family

10–3

Hot-Socketing Feature Implementation

July 2012

Altera Corporation

Cyclone III Device Handbook

Volume 1

Hot-Socketing Feature Implementation

Each I/O pin has the circuitry shown in Figure 10–1. The hot-socketing circuit does

not include CONF_DONE, nCEO, and nSTATUS pins to ensure that they are able to operate

during configuration. Thus, it is expected behavior for these pins to drive out during

power up and power down sequences.

Figure 10–1 shows the hot-socketing circuit block diagram for Cyclone III device

family.

The POR circuit monitors the voltage level of power supplies and keeps the I/O pins

tristated until the device is in user mode. The weak pull-up resistor (R) in Cyclone III

device family I/O element (IOE) keeps the I/O pins from floating. The 3.3-V tolerance

control circuit permits the I/O pins to be driven by 3.3 V before VCCIO, VCC, and VCCA

supplies are powered up, and it prevents the I/O pins from driving out when the

device is not in user mode.

1 Altera uses GND as reference for hot-socketing operation and I/O buffer designs. To

ensure proper operation, Altera recommends connecting the GND between boards

before connecting the power supplies. This prevents the GND on your board from

being pulled up inadvertently by a path to power through other components on your

board. A pulled up GND can otherwise cause an out-of-specification I/O voltage or

current condition with the Altera® device.

POR Circuitry

Cyclone III device family contains POR circuitry to keep the device in a reset state

until the power supply voltage levels have stabilized during power up. During POR,

all user I/O pins are tristated until the VCC reaches the recommended operating

levels. In addition, the POR circuitry also ensures the VCCIO level of I/O banks 1, 6, 7,

and 8 that contains configuration pins reach an acceptable level before configuration

is triggered.

Figure 10–1. Hot-socketing Circuit Block Diagram for Cyclone III Device Family

Output Enable

CCIO

Hot Socket

Output

Pre-Driver

Voltage

Tolerance

Control

Power On

Reset

Monitor

Weak

Pull-Up

Resistor

PAD

Input Buffer

to Logic Array

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