2 Serial Devices on one board

Read the data sheet for the sensors carefully.

Since you are a beginner, I will provide a little bit of terminology;

1. UART

Universal Asynchronous Receiver/Transmitter.

Also known as a serial port.

2. RS232

Level-shifted (and inverted) UART transmit and receive signals.

If your sensor data sheet states that the signals are logic level, eg., 3.3V signals, then the signals are the output of a UART. If the data sheet states that the signals are RS232, then they are level shifted, and will probably be +/-10V signals. Measure the signals with an oscilloscope and see.

If the signals are UART logic levels, then you can instantiate a pair of UARTs in the FPGA and control the sensors directly.

If the signals are RS232 levels, then you need a level translator, i.e., an RS232 level to logic level translator. The DE2 has a serial port - check the schematic and see if there are enough level translators on the DB9 for either one or both sensors. Sparkfun and other microcontroller online stores will have cheap boards with RS232 level translators and 100-mil header connectors that you can use.

Cheers,

Dave

IIRC RS232 should be +12v/-12v negative logic (-12v is a logic 1), however a lot of modern systems only drive a much lower range, possibly even +5v/0v!

However the receivers have to allow for the full voltage range.

Hi,

I didn't get a chance to look at the data sheets yesterday ... your comment about RS232 threw me off on the wrong track ...

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I am currently working on a project in which I need to connect two digital sensors, a Temp & Humidity sensor(SHT 15) and an accelerometer (ADXL345) both digital sensors. They also both use serial communications

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The ADXL345 can be accessed via either SPI or I2C, so the device can be connected directly to pins on the expansion header. The DE0-nano contains the ADXL345 device, so there should be examples you can use with that board.

The SHT15 sensor

http://www.sparkfun.com/datasheets/sensors/sht1x_datasheet.pdf

uses a non-standard serial protocol, which uses a serial clock and bidirectional serial data, where the data signal should only ever be driven low to avoid driver conflict. You will have to create a custom interface to this device, I'd recommend starting with bit-banged I/O, where the clock signal is driven as an output and the data controls the enable on a tri-state buffer that will drive low when enabled.

Both of these devices can be interfaced directly to your FPGA pins. You would not use an RS232 level translator.

Try coding up an interface, and if you have trouble, ask questions here on the forum.

Cheers,

Dave

So from what I have gathered from everyone's responses is that the ADXL345 is going to work well since I can connect to the SPI/I2C Core on the board using the expansion headers.

The SHT15 however, is not so nice since it will require me writing its own protocol in Verilog(I Assume?) ...

Sorry if this seems basic, but in our class we only scratched the surface of using the SPI and we were supposed to write our own protocol but the teacher scrapped that due to us falling behind.

Are the questions I'm asking clear? Should I just find another temp and humidity sensor to better work with the board, or that uses the standard protocol?

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The SHT15 sensor uses a non-standard serial protocol, which uses a serial clock and bidirectional serial data

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Oh yes sorry about that, the SHT15 doesn't use standard I2C. We are actually using a SHT2x in one of our projects, which does use I2C, and I just assumed the STH1x were the same.

You are write, you will have to write a custom component to access it, or as dave says use bit banged i/o, with PIOs for example.

If you really need the humidity you can try the SHT20 instead, that uses a I2C bus. If you only need temperature there are lots of other I2C sensors, such as the FM75.

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So from what I have gathered from everyone's responses is that the ADXL345 is going to work well since I can connect to the SPI/I2C Core on the board using the expansion headers.

The SHT15 however, is not so nice since it will require me writing its own protocol in Verilog(I Assume?) ...

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Yep, you've got it.

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Sorry if this seems basic, but in our class we only scratched the surface of using the SPI and we were supposed to write our own protocol but the teacher scrapped that due to us falling behind.

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Since you are not familiar with programming in HDL, then you probably want to find another sensor that has an I2C or SPI interface.

Cheers,

Dave

Ok, we have invested in a new SHT21 which uses I2C.

Now when building our system in SOPC builder, I have added a SPI(3-wire interface) for the ADXL345 under Interface Protocols->Serial->SPI(3 wire interface).

Setup:

Type-Master

Number of Selects-1

SCLK-4900000

Data width- 32 bits

Shift- MSB

Clock Polarity and Phase-0

My real question lies in the implementation of I2C protocol. I don't see a core for I2C implementation.. any advice? OpenCores.org?

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My real question lies in the implementation of I2C protocol. I don't see a core for I2C implementation.. any advice? OpenCores.org?

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The DE0-nano examples provided by Terasic use bit-banging to implement the I2C protocol. If you're going to use a NIOS II core, then that would be my recommendation.

I believe others have used the OpenCore's I2C core. Search the archive.

Cheers,

Dave

http://www.alterawiki.com/wiki/i2c_(opencores)

Or if you plan to use bit banging, all you need on the hardware side is a 2 port PIO.