AS3956_V01 datasheet(80/107 Pages) AMSCO

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[v1-11] 2018-Nov-14

AS3956 − Detailed Description

EEPROM Read and Write

The EEPROM can be accessed from SPI / I²C interface or over RF

field issuing NFC read and write commands. The EEPROM access

is controlled by the internal EEPROM controller. Since the

mutual access to the EEPROM is not possible AS3956 needs to

arbitrate between MCU and NFC device in cases of mutual

access. How this is handled it is defined according to arbit_mod

bit. EEPROM programing time is TEWS. Please note that word

data is sent MSB first which is opposite to the RFID EEPROM

programming where LSB is sent first.

Three interrupts can be triggered during EEPROM read or write:

• When EEPROM programing is executed successfully an

I_io_eewr interrupt is triggered.

• When EEPROM programming is terminated due to higher

priority of the RF part, writing to a non-existent address

or writing is not allowed an I_eeac_err interrupt is

triggered.

• When EEPROM is busy and can’t be accessed an I_acc_err

interrupt is triggered

Please note it is recommended when reading or writing to

EEPROM via SPI/I2C, the MCU should first check whether there

is enough energy available, then switch to Power mode 3 and

execute the SPI/I2C read or write and finally switch back to the

original power mode if required. In Power mode 3 the internal

supply is derived from VP_IO and not the field. Switching to

Power mode 3 will avoid that the supply voltage source for the

internal chip supply might be changed during an EEPROM

SPI/I2C read or write.

Also note that EEPROM does not contain any kind of

anti-tearing mechanism that would allow detection of

corrupted data

The valid range for the Block Address byte depends on the

EEPROM size. For 4kbit EEPROM, the valid range for the Block

Address byte is from 000_0000b to 111_1111b (EEPROM blocks

from 00h to 7Fh).

Data Buffer

Data in buffer is organized in bytes; each byte is terminated by

a parity bit. Data bits in a byte are numbered from b1 to b8

where b1 is LSB bit, LSB is sent first.

Data sent over SPI / I²C is also organized in bytes, bits in a byte

are marked D0 to D7, where D0 is LSB bit, MSB is sent first.

During reception, the framing engine checks the parity bit and

removes it from data frame, and only data bytes are put into

buffer. During transmission, the process is reversed, only data

bytes are put into buffer, while the framing engine adds the

parity bits.

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