Problems setting the TRF7970A EVM in PASSIVE TARGET mode

Hi to all,

You can see this Registry Bug Report

Danko Ivanov

 REPORT

OF

TRF7970A Registry problem

I. Problem description

Because of the needs of custom changes in some registers of the TRF7970A in order to be used with external power amplifier and detection circuit the following problem was found.

1. In the TI datasheet for TRF7970A is explicitly written:

6.1 Register Preset

After power-up and the EN pin low-to-high transition, the reader is in the default mode. The default configuration is ISO15693, single subcarrier, high data rate, 1-out-of-4 operation. The low-level option registers (0x02 to 0x0B) are automatically set to adapt the circuitry optimally to the appropriate protocol parameters. When entering another protocol (by writing to the ISO Control register 0x01), the low-level option registers (0x02 to 0x0B) are automatically configured to the new protocol parameters. After selecting the protocol, it is possible to change some low-level register contents if needed. However, changing to another protocol and then back, reloads the default settings, and so then the custom settings must be reloaded.

The Clo0 and Clo1 register (0x09) bits, which define the microcontroller frequency available on the SYS_CLK pin, are the only two bits in the configuration registers that are not cleared during protocol selection.

2. In the TI bug datasheet for TRF7970A  “ sloa159” is  written:

7.8 SPI With SS Pin Only – Some Registers Do Not Take Default Values

Description

Some of the registers do not take the default values when the appropriate protocol is chosen in the ISO Control Register.

Workaround

Manually program the default settings into the TRF796x during initialization.

3.In the TI sample program trf797x.c founded in SLOC250 lines for “Manually program the default settings into the TRF796x during initialization” are commented!!!

4.We found exact information in the datasheets for only two of the registers that are not affected from writing to the ISO register.

To be sure what really happens with the registers a small program was written, which sends to the PC HyperTerminal program trough the RS232 over USB chip FT232 registry contents.

In the following table1 are given the results. The time sequence is from the left to right.

Table1.

In table 2. are the results from the current program flow. Trf7970aINIT is our ini program for entering some custom values in the registry. The time sequence is from the left to right.

Table2.

It is seen that even after PWRON some of the important registers don’t take default values described in TI latest datasheet.

II. Conclusion

From the results is clear that only couple of the registers are particularly affected from the ISOCONTROLL register loading.

It will be necessary after setting the ISOCONTROLL register in the code, also set every particular register with the appropriate settings without believing on the PWRON settings also!!!

12. October 2012.                                                         Danko Ivanov

                                                                                    C.E.O.

                                                                                    Termotest Ltd.