I2C communication with USB 8451

I am measuring capacitance using AD7746. I have 10 such CDC's connected through two PCA9547 multiplexers(to avoid address conflict). Can I use USB8451 to collect data instead of a microcontroller. Also Is there is another DAQ with 2 wire I2C communication or is this the only one with I2C. Also is there some part with 10 I2C channels so I can collect data without using the multiplexer which adds complexity to code.

hello krtiruth,
If I understand your question correctly, you would like to know if the USB-8451 is a good choice for your particular chip( AD7746). As long as your chips allowing for different addressing, for you 10 different addresses, the 8451 can be connected to all the chips at once, an address each one individually through their particular address.This should allow you to not need the multiplexers to distribute communication to your various chips. As of right now the USB-8451 is the only I^2C device that National Instruments sells. Thanks again and have a great day!
Regards,
Nicholas K
National Instruments
Applications Engineer

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I2C Gyro NI USB-8451

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( You can look at my previous thread for reference)
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Solved!
Go to Solution.
Attachments:
I2C Read-INDIVIDUAL.vi ‏28 KB

Never mind got it right it was just unsigned bit instead of signed.

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elpiar wrote:
It's working!
Well, I realized I made a small mistake in the example. The number of bytes in the array constant should be 4, not 2. The device is full duplex, meaning you can write and read from it at the same time. The NI-845x SPI Write Read VI returns the same number of bytes as the number of bytes that were written. Thus, with just 2 bytes you will not actually get the current value of the register. You would get the values from the previous command. See attached mod.
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Attachments:
ADIS16400 XGYRO_OUT v2.vi ‏29 KB
ADIS16400 Burst Read Example.vi ‏36 KB

USB 8451 and PXI-2530B

Hi All,
I currently purchased the USB-8451 to use for the SMBus on a circuit board. The USB-8451 has only one port for I2C (SDA, SCL) needed for SMBus and my Board has two SMBus connectors for the Smart Battery control (Batt1(SCL1 and SDA1) and Batt2(SCL2 and SDA2)). I also have a PXI-2530B (Mux) and I would like to use this MUX(2530B) to switch either Batt1 or Batt2 to the I2C of the USB-8451. What wire topology will be the best to use and how should my connection look like. Any suggestion will be appreciated.
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Hi All,
I am using the USB 8451 I2C/SMBus to communication with my LTC1760 but have all kinds of issues. First, I added an external pull resistor of 4.3kOhms but still have commucation issue. What I am trying to do is simulate a smart battery charging. I set my clock to about 80kHz and my slave address is 0x14 (LTC1760). These are the few errors that I get:
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Attachments:
LTC1760-SmartBatterySystem-using SMBus.pdf ‏371 KB

Reading spi shift register bit with NI 8451

Hello
we are proposing to use SPI communication with NI 8451.
we would like to know as how we could find whether the SPI shift Register bit has been set and also is there any direct means of
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Thanks
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Hello Bhavani,
The USB 8451 does have DIO lines available and can be programmed by the SPI output. Please see the USB-8451 User Guide and Specifications for more information about that. If you have any more specific questions, please let me know.
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USB-8451 + EEPROM

Hi There,
I trying to replace my standard interface PCB (with MicroChip) with USB-8451 to communicate with EEPROM.
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Hi Norman,
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Need help - I2C write/read with TAOS TCS3414 light sensor using USB-8451

Hello, I'm new to labview and need help setting up a vi that will allow me to communicate with a digital light sensor (TAOS TCS3414) using a USB-8451. I need to use the sensor to measure light from a light source that I designed and built as part of a project im working on. I've tried looking at several labview I2C exampled but find them to be very confusing. I've used an arduino to interface with the sensor successfully but need to use labview and dont understand how to write the program. The actions are simple; I need initialize the sensor with a simple command and then request data from 8 data registers and then read that data. The data will then be used in further calculations. The portion i need help with is writing and reading from the sensor. I've attached the datasheet for the sensor as a guide. I can also provide the arduino code that i use to read data from the sensor if that would help.
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Attachments:
TCS3414_Datasheet_EN_v1.pdf ‏1806 KB

Hi Aaron,
Here you go, this is made with a USB-8452.
When you run the code tick the power en dac enable box on.
Maybe you can help me with my problem, I want to use a fiber to sense light from a led.
Do you use any fiber hardware with the TCS3414?
gr,
Attachments:
TCS3414.vi ‏63 KB

USB 8451 simultaneous I2C and IO

Hi,
I am using the NI USB8451 to communicate with a TI BQ77910A by I2C. The I2C communication works for reading right now but in order to write in the EEPROM registers I need to provide 3.3V using the IO signals.
I've tested the IO and generated a signal successfully. My question is: is it possible to simultaneously run I2C and IO on the USB8451. Do they need to be on the same VI in order to operate?
Thanks,
Vid
Solved!
Go to Solution.

Yes it works with the NI USB 8451. Though it is worth mentioning only ports P.04 to P.06 are capable of delivering a true steady output voltage of 3.3V. The other ports seem to struggle in my experience but it is not a bad thing considering that the NI8451 is supposedly only capable of delivering 3.3V.
Thanks,
Vid

USB 8451 - SMbus with labview: help please

Dear all,
I just purchased an USB 8451 and I need to interact with a smart battery using a labview interface. I really need a departure point to build up a VI read/write and finally interact with the battery, and the tutorial on NI website ( http://www.ni.com/white-paper/5767/en/) seems not too exhaustive to me. I set the I2c configuration property node as specified, but I have some doubts on the adress to put, is it really 1010000 for the smart battery (it is my only slave)... Once this is solved, how to "ask questions" to the battery?
Could anyone who had the same problem than me post a complete VI I can use as starting point?
It seems like I must gather much more information about this topic, so, please, any suggestion on how to interact with the battery is welcome....

Yep, the problem is definitively the adress of the slave (smart battery), which I set to 1010000 as specified in the NI tutorial, but that is not correct, because this is the error message I get when trying to read two bytes:
Possible reason(s):
NI-845x: The slave did not acknowledge an address+direction byte transmitted by the I2C master. If you are using ACK polling, consider increasing the timeout. Other reasons include the incorrect address set in the I2C configuration or the incorrect use of the 7-bit address. When entering an address to access a 7-bit device, do not include the direction bit. The NI-845x Basic I2C API internally sets the direction bit to the correct value, depending on the function (write or read). If your datasheet specifies the 7-bit device address as a byte, discard the direction bit (bit 0) and right-shift the byte value by one to create the 7-bit address.
I also attach my VI
Attachments:
SMbus reading.vi ‏12 KB

USB 8451 I2C acknowledge bit problem

Hello,
I'm in the middle of developing a I2C interface for a Xilinx Vertex-5 evaluation board. This is a standard Philips I2C interface and I'm able to view the SCL and SDA lines and everything looks like it should be working but I'm not getting the acknowledge returned on the SDA line.
We have flags output on other pins and the acknowledge is working but it seem the SDA line isn't releasing the line to allow the acknowledge to go low.
I have tired the write program examples that came with 8.6 but they are for a serial PROM and I don't believe serial PROM return an acknowledge during programming. I have also tried the example from the "Using I2C with LabVIEW and the USB-8451" and even though all the clocks and data looks good at the proper pins the acknowledge bit stay high.
The Discussion Forum has a similar question about acknowledge on a "smbus_Read_Block" (11-9-06) where "newbieLBW" ask about this for a block read. I have tried that example and created it for a write but I'm still not getting a acknowledge bit to go low.
I have attached my I2C development vi that is just to prove functionality. And the write routine is in case loop 2.
Solved!
Go to Solution.
Attachments:
I2C PortCofig_3.vi ‏70 KB

Matt,
Yes we have verified that the Xilinx is getting the information it needs and it returning a acknowledge pulse on the 9th SCL clock pulse. I see this because we brought out the signal to a extra pin on the connector along with start and stop flags to make sure things inside the Xilinx were seeing the input properly. When I run this program in a debug mode and highlight the data path the only errors I received is from the 'run script' function when the 8451 tried to write the address.
Quick question for you. I had mention a discussion forum question about the acknowledge bit on a smbus which is quite like the I2C interface. In that
example the read multi-byte function starts with a create script, script clock rate,script issue start, address+write, script write, then another script issue
start, then it go on to another address+write. My question is, it seem to me that nothing happens on the I2C SDA line until your data enters the 'run script'
and I'm not seeing why they have two starts without a run. I have tried to duplicate the multi read front section to see what it does but mine doesn't seem
to run in as much as the SDA line never starts unless I have the run script in the read path. My understanding is that the 'script start and address+write are
just setup for the run script and without the run script nothing executes. Yes or No?
I want to thank you for taking the time to view this question I have. The purpose for this interface is a future chip we are designing and we are using the I2C for reading and writing control registers within the chip. I need to get the development platform working before I move onto the full interface and all the registers are 32 bits wide so I'm going to have to do all multi-byte reads and writes.
I hope I have answer some of your question and will be looking forward to any information you can pass along. I'm going to be out of the office until the 28th but I'll keep and eye on this forum from home where I'll be working on the full interface design but without the read and writes for now.
Merry Christmas and the Happiest of New Years to you and your family!
Gary Tyrna
Tahoe RF Semiconductor, Inc.

How to isolate USB-8451, I2C/SPI Interface

How can I protect the SCL & SDA lines on a USB-8451 from overvoltage? The User Guide says:
Caution Take special care with respect to the I2C SDA and SCL lines. To allow for external
pull-ups, the circuit protection has been removed. Do not exceed the specified voltages for
these signals.
I've had several instances where my UUT applied 28 volts to one/both of these lines and destroyed my I2C interface. What can I do to protect these lines?
Jim
Jim
You're entirely bonkers. But I'll tell you a secret. All the best people are. ~ Alice

There are several ways to this. I often use this simple circuit is based on zener diodes and the basic idea is quite similar to some commercial circuits also. The zener diode react quite fast to the surges. Zener diodes also have Low capacitance, so they are suited for high speed data lines. Unfortunately the surge capacity of those zener diodes is not very high, so that they can't handle the large spikes by themselves. That's why I have added 10 ohm resistors in series with data line before the zener diodes. This resistor limits the surge current to safer value for zener diode. The resistor must be always be between the data line and zener diode, so you must plug this circuit in the way where the computer goes to the connector on the right and the data line to the connector on the left. It is possible to make this circuit "bidirectional" just by adding also resistors to the computer side of the zener diodes, but this increased the series resistance in the data line.
As mentioned there are more advanced circuits. Like active circuits. As an example the ADG467BR. Another option is Zener Transient voltage suppressors like the P6KE11CA. The P6KE11CA is bipolar so you only need 1 diode. But for a low voltage system like yours the zener solution may work fine. Remember to select a zener which can handle the current. If you 28 volt and use a 10 ohm resistor the current will not be higher than 28/10 ampere as a thumb rule. Probably lower.
Message Edited by t06afre on 01-23-2009 03:41 PM
Besides which, my opinion is that Express VIs Carthage must be destroyed deleted
(Sorry no Labview "brag list" so far)
Attachments:
sample.PNG ‏2 KB

USB 8451 for I2C

Hello,
I am looking for a starting point.
My problem is I need to communicate with the PCA9555 (http://focus.ti.com/lit/ds/symlink/pca9555.pdf). I have searched the NI website and have come across a USB-8451 that seems to be the answer to my problem. However, I need to also measure current and this device seems to lack that ability.
First off, would this be the device I would want to use to communicate via I2C? The only reason I question this is because I cannot access the examples that would give me a good sense that I found what I was looking for.
Secondly, is there a device like this offered by NI that would be able to communicate via I2C and be able to measure current? Or do I have to purchase 2 separate devices?
Thirdly, is there anybody out there who has encountered the same problem (possibly with the same PCA9555)?
Thank you,
Gerardo Hernandez
Solved!
Go to Solution.

Hello,
I have a USB-8451 on my desk in use, and for ease of use in LabVIEW, you cannot beat it; some example code from one of my apps:
Here I am just transmitting an constant sequence (an initialisation sequence for my hardware) to a Slave with address 112 (actually an I2C bus all-call address for my devices).
If you want to keep things easy, I would suggest 2 seperate devices, one being a USB-8451. You can bit-bang I2C, etc at the cost of complexity and dev time.
Mark B
===If this fixes your problem, mark as solution!===

Usb 8451 I2C

Hi,
I am using LabView 8.0 with an NI USB 8451 I2C device. The problem I'm
having is once a DUT fails it causes the next DUT to fail also. Very
repeatable. Its as if there is a buffer that still has some data in it
from the first failure or an error flag has been set. I have to restart
the program to clear up the problem. I'm not sure if its a LabView
error flag or an I2C "buffer" problem. Also, is there a way to
initialize the 8451 so I can always start from a known good status? I
have the same problem with the GPIB driver and the HP meter buffer but
I've done a workaround by reading the meter twice. The first read is
garbage but it clears the HP buffer so the second read is valid.
Thanks in advance for your help.
Larry Clifford
Precision Linear Systems

I had the same problem in 8.2 that I was never able to resolve. Is the 8451 the only master on the bus or are you tapping into a line that already has a master? I found the 8451 worked very well when it was the only master but problems popped up on a multi-master setup. I contacted NI tech support and they assured me the 8451 adheres to the I2C multi-master specs. Scope traces I took seemed to verify that. I believe the problem was that the native master on the bus didn't handle multi-master mode correctly.
Link to thread

I2C communication with USB 8451

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