TMS37157 datasheet(29/47 Pages) TI

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MSB

LSB

CC=00:

Transponder AccessCommand(TAC)

CC=01:

n.a.

CC=10:

EnhancedCommands(EC)

CC=11:

ReservedCommands(RC)

X:Don’tcare

TMS37157

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SWRS083A – SEPTEMBER 2009 – REVISED NOVEMBER 2009

If an error occurs during SPI communication, the BUSY line remains at the level it was when the error occurred.

The following three types of error are possible:

Error 1:

The TMS37157 stops communication via its SPI interface and indicates this by taking BUSY low. The microcontroller

has not finished, but BUSY remains low.

Error 2:

The TMS37157 is ready to continue communication via its SPI interface and indicates this by taking BUSY high. The

microcontroller has finished, however, and expects BUSY to remain low. After max. 50ms = tBusyhigh an internal

watchdog shuts down the whole TMS73157 IC.

Error 3:

If the TMS37157 receives an invalid command it performs a power down command. This command results in a shut

down of the whole TMS37157 IC.

SPI Protocol Structure

The first 8 bits sent by the microcontroller contain telegram length information (LEN), which defines the number

of following bytes to be transferred via the SIMO line. It is the number of bytes excluding the LEN-byte.

The second 8 bits sent by the microcontroller contain the Command byte (CMD). The first (most significant) two

bits of the Command byte determine which of the four different types the command is, and the six least

significant bits contain various flags associated with the command (see Figure 21).

Three types of command are available:

•

Transponder Access Command (TAC)

•

Enhanced Command (EC)

•

Reserved Command (RC) – for future use.

Figure 21. SPI Command Byte Overview

NOTE

All SPI bits that are either not used or are marked with an "X" are reserved for future

use and must be "0".

Transponder Access Commands

The microcontroller can access the contents of the Transponder Memory by sending the TMS37157 a

Transponder Access Command via the SIMO line.

The two most significant bits of the Command byte determine the Transponder Access Command and the six

least significant bits are don’t care. If the contents of the Command byte are invalid for the device configuration,

an error condition will be indicated via the BUSY line.

This command is followed by the same Write Address used in LF data transmissions and, if necessary, is

followed by further data bytes (e.g. Selective Address, Data). The TMS37157 responds by transferring the

relevant transponder data to the microcontroller via the SOMI line (see Figure 20.)

In all cases, responses to Transponder Access Commands are sent without the 16-bit preamble, start byte and

BCC that are normally used in LF data transmissions.

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