AT43USB325 datasheet(11/109 Pages) ATMEL

11 / 109 page

3355C–USB–4/05

AT43USB325

between the two versions is with respect to the serial EEPROM interface pins, GPIO PF[0:3].

The differences are:

3.4

SPI Serial EEPROM Interface (AT43USB325E Only)

The AT43USB325E is designed to interface directly with a synchronous serial peripheral inter-

face (SPI) SEEPROM such as the Atmel AT25HP256/512. All instructions, addresses and data

are transferred with the MSB first and start with a high-to-low SSN transition.

Note:

The SPI port of the AT43USB325E at PF[0:3] is dedicated for program memory downloading only.

It cannot be accessed by the firmware program.

Figure 3-1.

AT43USB325E Read Sequence

3.4.1

Read Sequence

The AT43USB325E asserts its SSN output pin and outputs a 3 MHz clock at SCK. It

continues to activate SCK until the completion of the read process.

The AT43USB325E transmits the READ opcode (= 0000011) through its MOSI, fol-

lowed by the 16-bit byte address to be read, x0000. Please note that the

AT43USB325E will send a 16-byte address only. SEEPROM with SPI that requires a

24-bit address cannot be used with the AT43USB325E.

The SEEPROM then shifts out the data through its MISO pin.

The AT43USB325E de-asserts SCK and SSN after 16K bytes data read is complete.

Figure 3-2.

READ Timing

Port F Pins

AT43USB325E

AT43USB325M

PF0

Slave Select Pin – Its output will be asserted (low) during

downloading of firmware and will stay de-asserted (high) after

download is completed.

NC (No connect)

PF1, PF2, PF3

Functions as serial EEPROM interface signals during

downloading and as GPIO pins after download is completed.

GPIO

AT43USB325E

AT25HP256

SSN

MOSI

MISO

SCK

10112021222324252627282930

...

DATA OUT

MSB

HIGH IMPEDANCE

INSTRUCTION

BYTE ADDRESS

SCK

MOSI

MISO

SSN

AT43USB325 Datasheet(PDF) 11 Page - ATMEL Corporation

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