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[v1-04] 2016-Feb-03

AS3955 − Detailed Description

Writing and Reading of EEPROM Through SPI

EEPROM data can be read and written also through SPI

interface. Due to possible conflict with the RFID interface

additional arbitration bit can be set (IC_CFG0) in order to set

the priority access to the EEPROM access. If EEPROM write

operation is terminated due to higher priority of the RF an I_

acc_err (Interrupt Register 1) IRQ is sent. The description is

referring to following case when an EEPROM write operation is

triggered via SPI / I²C and bit arbit_mod (EEPROM, IC_CFG0,

bit3) is set to 1 which means that RF has priority over SPI when

accessing EEPROM. In this case EEPROM via SPI / I²C write will

be terminated and IRQ I_acc_err is triggered if tags enters RF

field and EEPROM is needed for RF initialization, EPROM read or

write is issued via RF.

Word Address Byte

Both EEPROM modes (Read and Write) use Word Address byte

to define the address of the EEPROM word which is accessed.

Seven MSB bits of the Address Byte are used to define the

address; while the last bit is don’t care (it is used to synchronize

EEPROM access).

Figure 63:

EEPROM Block Address Byte

EEPROM Write

In order to program an EEPROM block, six bytes shall be sent

(mode byte, block address byte and 4 bytes of data, all of them

MSB first). Actual EEPROM programming is started with rising

/SS edge signal which terminates the EEPROM Write command.

EEPROM Read

In order to read data from EEPROM, first a mode byte is sent,

followed by the block address byte (MSB first). Then one or more

blocks of data with address auto-incrementing (packets of 4

bytes) are transferred to MISO output, also MSB first. MOSI is

sampled at the SCLK falling edge; data to be read from AS3955

EEPROM is driven to MISO pin on SCLK rising edge and is

sampled by the master at the SCLK falling edge. In case the

block on the defined address does not exist, all 0 data is sent to

MISO.

Please note that SCLK frequency should not exceed 1MHz

during EEPROM Read (limited by EEPROM read access time).

EEPROM Block Address

WA6

WA5

WA4

WA3

WA2

WA1

WA0

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