Txs0108E on ZC702

Hi Winston,

TXS0108E will support 60Mbps data rate. If the SPI clock is more than 30MHz, the speed will be out of the device range.

Could you please decreas the SPI clock frequency to be less than 30MHz?

Thanks

Wei

The spi clock is about 30 MHz. The spi data and select lines are also distorted. The spi select is high for about 80 ns and low for about 700 ns.

Winston

Do the TXS0108E parts require pull-up resistors on the outputs?

Winston

there is internal pull-up 10k resistor in TXS0108E. Any pull down resistor on FPGA I/O?

Wei

The fpga pins are set as always output with no pull up or pull down.

Winston

I slowed the signals down to less than 1 MHz and the txs0108 output still looks terrible. I guess the chip could be blown but when I routed the spi bus to the second interface circuit it looked about the same.

Winston

The input to the txs0108 has about 0.7 V of ringing on both edges. Could that be confusing the direction control? Or could it be the reflections on the output?

Winston

Wei,

I have not resolved this issue yet. Do you have any suggestions? What is the difference between the txs0108 and the txb0108?

Winston

Wei,

This is the input and output waveforms of the TXS0108 on the ZC702 board with no load. What do you suggest?

Winston

Hi Winson,

For TXB serilal, it can support higher data rate signal than TXS andTXB is better to be used in push-pull I/O. When TXB is used, exteranl pull-up or pull-down resistor should be removed since there is a 4k serial resistor on each I/O.

For TXS serial, It can used in open-drain and push-pull I/O system. There is a 10k pull-up resistor on each port. Thus, If pull-down resistor is added on the port, it will decrease I/O DC voltage.

For this issue,Could you zoom in the output rise edge?  It will help to analyze the issue.

Thanks

Wei

Wei,

I tried replacing the txs with a txb but it did not improve the situation. Both traces are from the txb0108. The settings  for this trace were 5 nsec/div x 1 V/div. The previous one was 5 usec x 1 V/div.

Winston

Wei,

VCCA of the TXB0108 is wired to 2.5 V. VCCB is wired to 3.3 V. There are 0.1 uF caps on both power pins and OE is wired to 2.5 V.

Winston

Wei,

You asked me to post higher resolution scope traces. Have you had a chance to look at them yet?

Winston

Hi Winston,

The reason could be greater driver and transmit line effect. Please decrease FPGA output driver and add serial 33ohm resistor which should be close to TXB0108.

Thanks

Wei