SN74AVC4T774: Connect to two devices.

Jerry Chu

Part Number: SN74AVC4T774
Other Parts Discussed in Thread: SN74LVC245A

Hi Expert,

I want to use one SN74AVC4T774 IN SPI application and connect to two slave device. One slave device is close to CPU and 20CM for second device. How do you suggest to connect first device? Between CPU and SN74AVC4T774 or after SN74AVC4T774?

BTW, SN74AVC4T774 shows it's a tri-state output IC, it means can without the pull high resistor, right? Thanks!

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 96591 points

Can you provide a schematic? I'm not entirely sure what you mean.

0 Jerry Chu over 6 years ago in reply to Emrys Maier

Genius 4915 points

Hi Emrys,

FYI. Thanks

0 Clemens Ladisch over 6 years ago in reply to Jerry Chu

Guru 243220 points

In option 2, the CS signal and the other SPI signals will have different voltage levels. I assume the EEPROM supports that?

When an output is tri-stated, that signal line is floating unless you're using a pull-up resistor.
Why do you want to disable the outputs?

0 Emrys Maier over 6 years ago in reply to Jerry Chu

TI__Guru* 96591 points

Hi Jerry,
Since this is a voltage translation question, it would be very helpful to know the voltages at each device in the system. I'm assuming, as Clemens mentioned, that the "Module" is at a different voltage than the "CPU" in this block diagram, so at what voltage does the "EEPROM" operate?

0 Jerry Chu over 6 years ago in reply to Emrys Maier

Genius 4915 points

Hi Emrys,
The voltage both are 1.8V. The CPU output capability is only around 4 inch, SN74AVC4T774 is be use like a buffer.

0 Emrys Maier over 6 years ago in reply to Jerry Chu

TI__Guru* 96591 points

I understand.

The part you have selected is a voltage translator. We have a huge variety of direction controleld buffers (transceivers) available depending on your requirements.

If you just want a suggestion of a transceiver that operates at 1.8V, I would say to use SN74LVC245A.

In this case, I would recommend going with option 1 - this will minimize capacitive loading on the transceiver and will improve signal quality.

0 Jerry Chu over 6 years ago in reply to Emrys Maier

Genius 4915 points

Hi Emrys,

If in option one, the EEPROM MISO will connect to A2, seems will cause the SN74AVC4T774 abnormal. Do you have idea for it? Thanks!

0 Emrys Maier over 6 years ago in reply to Jerry Chu

TI__Guru* 96591 points

"abnormal" can describe a very wide variety of issues. Do you have a scope shot of the problem?

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SN74AVC4T774: Connect to two devices.