ST25R200 datasheet(67/88 Pages) STMICROELECTRONICS

67 / 88 page

5.15.2

Stop all activities

This direct command stops any ongoing activity:

•

Performs clear FIFO command

•

Stops data transmission and reception

•

Stops all timers

•

Clears IRQ line and IRQ status bits

This command does not update any register apart from the FIFO status registers. Therefore, it does not disable

the field in case it was enabled.

5.15.3

Clear FIFO

This direct command clears FIFO pointers and FIFO status registers. It does not clear the IRQ line or IRQ status

bits.

Ahead of a transmission it sends this command before writing data into the FIFO. If a clear FIFO command is sent

during an ongoing data transmission, then the data transmission is aborted and the FIFO status registers are

cleared.

5.15.4

Clear Rx gain

This command initializes both the AGC and squelch blocks and it resets the gain reduction to the value set in

afe_gain_rw<3:0>.

Sending this command also stops any ongoing squelch process.

5.15.5

Adjust regulators

This command adjusts the VDD_RF (and VDD_A) regulator voltage drop as defined in the regd<2:0>. Using this

method the PSRR is optimized and the maximum available driver supply is used.

Before executing the command the bit reg_s must be cleared, the transmitter (tx_en) and receiver (rx_en) should

be enabled, so that the adjustment is executed at realistic load conditions.

When the adjustment starts the VDD_DR is set at maximum, and then stepped down successively until it reaches

the desired drop defined in bits regd<2:0> or no more steps are available.

Adjustment result available in the regc<4:0> bits.

5.15.6

Transmit commands

The transmit commands (transmit data and transmit EOF) are used to start a data transmission from the

ST25R200.

They switch the device to reception mode after the transmission is completed.

Prior to executing the command transmit data, the direct command

Clear FIFO shall be sent, followed by the definition of the number of transmitted bytes/bits, the data to be

transmitted written into FIFO, as well as all configuration parameters (for example, protocol mode, bitrate, CRC,

parity, framing, etc.) set.

For the direct command transmit EOF, the ISO15693 mode shall be set and it is not necessary to send the direct

command clear FIFO before as the FIFO is not used.

At the end of the transmission an I_txe is produced, and the device moves into reception mode.

5.15.7

Mask receive data and unmask receive data

The mask receive data direct command disables processing of the receiver output by the Rx decoders, and AGC

operation.

The unmask receive data direct command enables processing of the received data by the Rx decoders and AGC

operation.

A common use of this command is to re-enable the receiver operation after it was masked by the command mask

receive data. If the mask receive timer is still running while the direct command unmask receive data is received,

reception is enabled, and the mask receive timer is reset.

ST25R200

Application information

DS13658 - Rev 2

page 67/88

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