ENC28J60-CSLASHSP datasheet(7/96 Pages) MICROCHIP

7 / 96 page

Preliminary

DS39662B-page 5

ENC28J60

2.0

EXTERNAL CONNECTIONS

2.1

Oscillator

The ENC28J60 is designed to operate at 25 MHz with

a crystal connected to the OSC1 and OSC2 pins. The

ENC28J60 design requires the use of a parallel cut

crystal. Use of a series cut crystal may give a frequency

out of the crystal manufacturer specifications. A typical

oscillator circuit is shown in Figure 2-1.

The ENC28J60 may also be driven by an external clock

source connected to the OSC1 pin as shown in

Figure 2-2.

FIGURE 2-1:

CRYSTAL OSCILLATOR

OPERATION

FIGURE 2-2:

EXTERNAL CLOCK

SOURCE(1)

2.2

Oscillator Start-up Timer

The ENC28J60 contains an Oscillator Start-up Timer

(OST) to ensure that the oscillator and integrated PHY

have stabilized before use. The OST does not expire

until 7500 OSC1 clock cycles (300

μs) pass after

Power-on Reset or wake-up from Power-Down mode

occurs. During the delay, all Ethernet registers and

buffer memory may still be read and written to through

the SPI bus. However, software should not attempt to

transmit any packets (set ECON1.TXRTS), enable

reception of packets (set ECON1.RXEN) or access any

MAC, MII or PHY registers during this period.

When the OST expires, the CLKRDY bit in the ESTAT

this bit as necessary to determine when normal device

operation can begin.

XTAL

OSC2

RS(1)

OSC1

RF(2)

To Internal Logic

Note 1:

A series resistor, RS, may be required for AT

strip cut crystals.

The feedback resistor, RF , is typically in the

range of 2 to 10 M

Ω.

ENC28J60

3.3V Clock from

External System

OSC1

OSC2

Open(2)

Note 1:

Duty cycle restrictions must be observed.

A resistor to ground may be used to reduce

system noise. This may increase system

current.

ENC28J60

Note:

After a Power-on Reset, or the ENC28J60

is removed from Power-Down mode, the

CLKRDY bit must be polled before

transmitting

packets,

enabling

packet

reception or accessing any MAC, MII or

PHY registers.

ENC28J60-C/SP 数据表(PDF) 7 Page - Microchip Technology

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