TMC423-TMC428 interconnection - why tie 428 SDO to 423?

[krunal_299]

Is it not always necessary to connect these 2 pins of 423 to the 428.
it depends on application , am i right?
oh, can you pls explain me in detail with any example if it is possible 4 u?
with warm regards!
krunal.

[TRINAMIC_BD]

Exact. The TMC423 just provides a 74hc125-like Tri-State gate at these pins, in order to allow sharing of SPIOUT (MOSI line) with the TMC428, which does not Tri-state its SPI output.

Please find the updated TMC423 datasheet on our website.

[krunal_299]

ok i got what u said.
With the configuration shown in fig.4 of 423 datasheet, will it be possible to read the any register of 428 by microcontroller.
if yes, then how?
my ultimate question is how i can maintain the sequence of SPI data by microcontroller between 423 and 428?

[TRINAMIC_BD]

You can still access both completely on their own - they keep their own SPI chip select lines, and thus do not interfere with each other.

[krunal_299]

Ok
As per the block diagram figure of 423,
when i activate the nSCS_C of 428 (connected to NSCS428 of 423),
the SDO428pin of 423(connected to SDO_C of 428) get multiplexed with SDO pin of 423.
ultimately microcontroller can access the 428 data via SDO pin of 423.

This is my perception got from datasheet, is it ok?

[TRINAMIC_BD]

Yes, correct.