PCA9515B fails to forward ACK

Simon Steinegger

Other Parts Discussed in Thread: PCA9515B, TCA9517

The following screenshot shows my problem. C1,C2 (zoom Z1,Z2) show the slave side of the I2C-repeater. C3,C4 (zoom Z3,Z4) show the master side. The slave properly ACKs address 0x50 as well as the following Data 0x01 but only the latter is forwarded by PCA9515B. It seems PCA9515B generates a NACK by itself for no reason. Or, another way of seeing it, PCA9515B only forwards the ACK, if the 8^th bit was HIGH (Address 0x51 would be ACKed, Data 0x02 would be NACKed).

What is the reason for this behaviour? Am I missing something?

Thanks for your inputs

Simon

over 9 years ago

0 Siby James over 9 years ago

TI__Expert 5140 points

Hi Simon,

We are currently looking into this for you. Thank you.

Siby

0 Simon Steinegger over 9 years ago in reply to Siby James

Prodigy 170 points

I think I found my problem. According to the datasheet (p.8) "Two or more PCA9515B devices cannot be used in series.". I don't - BUT I have an ISO1540D in series which seems to make use of the same mechanism to prevent lockup conditions. So I'm afraid I need to find a way to get along without one of those.

Thanks anyway for your efforts so far!

0 Jonathan Valdez over 9 years ago in reply to Simon Steinegger

TI__Genius 16510 points

Hello Simon,

You are correct. A static offset is what prevents a series connection, and it is the most common method used by translators/buffers to prevent a bus latchup condition.

One thing worth noting, is that the TCA9517 allows for series connections, as long as 2 static voltage offset sides are not placed on the same side (for example, if you had 2 TCA9517s, you cannot connect the two B sides)

0 Simon Steinegger over 9 years ago in reply to Jonathan Valdez

Prodigy 170 points

Thanks for the recommendation. This will certainly be worth a try.

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PCA9515B fails to forward ACK