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[v1-04] 2016-Feb-03

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AS3955 − Detailed Description

Interface Arbitration

Concurrent access to AS3955 internal EEPROM from RF or SPI /

I²C requires arbitration, to resolve conflicts or undesired

behaviour.

AS3955 implements two arbitration modes, which can be set in

Configuration Byte IC_CFG0.

Arbitration Mode 0

AS3955 arbitrates EEPROM write accesses according to

first-come-first-serve principle.

• In case no write access is currently ongoing, both RF and

SPI / I²C interfaces are allowed to write into EEPROM.

• In case a write request comes over RF, while SPI / I²C is

writing, AS3955 will return a NAK.

• In case a write request comes over SPI / I²C while RF is

writing, AS3955 will trigger a I_err_acc interrupt (see

Figure 94).

Arbitration Mode 1

AS3955 gives always priority to RF accesses. In this mode,

AS3955 behaves over RF as a pure contactless tag.

• In case SPI / I²C is performing a EEPROM write while the

RF field is turned on, the write operation is interrupted to

allow the initialization of the RF communication

• In case the RF field is already on and SPI / I²C performs a

write to EEPROM and a READ or WRITE command is

received via RF, the write operation of SPI / I²C is

interrupted so that the RF operation can be performed

In both cases, a I_err_acc interrupt (see Figure 94) will be

triggered.

Please note that the interruption of an EEPROM write may result

in an undefined or “weak” state for the cell being programmed,

and a second successful write attempt is suggested.

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