AT43USB355 datasheet(10/115 Pages) ATMEL

10 / 115 page

AT43USB355

2603G–USB–04/06

The program memory of the AT43USB355E is automatically written with data stored in an

external serial EEPROM during the chip's power-on reset sequence. The power-on reset is

the only way the on-chip program memory of the AT43USB355E will be written or modified.

The two versions of the AT43USB355 are binary compatible. A firmware written for the

AT43USB355E will work unaltered on the AT43USB355M. The only functional difference

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

The differences are:

SPI Serial

EEPROM Interface

(AT43USB355E

Only)

The AT43USB355E 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 AT43USB355E at PF[0:3] is dedicated for program memory downloading

only. It cannot be accessed by the firmware program.

Figure 4. AT43USB355E Read Sequence

Read Sequence

The AT43USB35E 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 AT43USB355E transmits the READ op-code (= 0000011) through its MOSI, fol-

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

AT43USB355E will send a 16-byte address only. SEEPROM with SPI that requires a

24-bit address cannot be used with the AT43USB355E.

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

The AT43USB35E de-asserts SCK and SSN after 24K bytes data read is complete.

Port F Pins

AT43USB355E

AT43USB355M

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

AT43USB355E

AT25HP256

SSN

MOSI

MISO

SCK

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