MC33690 Standalone Tag Reader Circuit, Rev. 5

Standalone Configuration with Two-Wire Bus

Freescale Semiconductor

12

8

Standalone Configuration with Two-Wire Bus

When a low level is applied on MODE1 and a high level on MODE2, the circuit is in configuration B (see Figure 25). The K

pin is set as an output sending the demodulated data.

The AM pin is set as a VSUP referenced input pin receiving the amplitude modulation and the shutdown/wake-up commands.

Forcing high and low levels on AM achieves the amplitude modulation by switching on/off both antenna drivers. This amplitude

modulation can be monitored on the K output and allows antenna short and open circuit diagnosis. The circuit can be put into

standby mode by forcing the AM line at zero during more than 2 ms. The circuit sends an acknowledge pulse before entering

into standby mode.

In standby mode, the oscillator and most of the internal biasing currents are switched off. Therefore, the functions (tag reader

and ISO 9141 driver) are inactive except for the voltage regulator and the ISO 9141 receiver on pin AM. The driver output TD1

forces a low level and TD2 a high level. A rising edge on AM wakes up the circuit. After completion of the wake-up sequence,

the circuit is automatically set in read mode.

In configuration B, DOUT and Rx outputs always force a low level and Tx is disabled.

Figure 8. Modes Access Description in Two-wire Bus Configuration

Figure 9. Configuration B State Diagram

AM line

1

0

0

0

1

1

data read

drivers off

AM line

t Š T1

standby mode

Read and write sequences:

1

0

0

0

1

1

K line

Entering into standby mode:

K line

data write modulation

data write

AM line monitoring

drivers on

wake-up sequence

data read

T2

T2

T1

Coming out of standby mode:

AM line

K line

standby mode

acknowledge

TD1/2 off

TD1/2

Standby

AM line high

Wake-up

AM line low

T1 £ AM line low

Reset

AM line high

AM line low

AM

switching