AS3955 datasheet(16/111 Pages) AMSCO

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[v1-01] 2015-Apr-29

AS3955 − Detailed Description

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 92).

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 92) 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.

Energy Harvesting

AS3955 has energy harvesting capability. The regulated voltage

output pin for energy harvesting is VP_REG. The energy

harvesting is enabled only in Power Mode 1 and 2. The output

voltage and resistance can be set by Configuration Byte

IC_CFG1.The energy harvesting can be disabled by setting the

output resistance register to 0 as shown in Figure 15.

Figure 15:

Output Resistance Settings

Figure 15 shows settings of the regulated voltage output. The

output can be set between 1.8V and 4.5V in 100mV step.

rreg<1:0>

Output Resistance

Comment

00b

Disabled – output pin

is in tristate

01b

100Ω

10b

50Ω

11b

25Ω

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