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Can the I2C API be used without a subaddress/register address step?

Question asked by Ben Burch on Jun 14, 2019
Latest reply on Jun 17, 2019 by Ben Burch

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Hi!

I am using an NXP-824 to drive a radio device. The device does not have any register addresses defined, and wants to just send a group of bytes based on a function code (which is not in the right place to pretend to be a register address) and I cannot seem to get the API to not try to send the register address to the device.

Is it possible with the standard API?

Is there a modified version of the API that is without subaddress?

A bit of googling suggests that others have hit this snag, so I am hoping one of you has some advice.

Thanks!

-BenBurch

BTR Controls, Inc.

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Sabina Bruce

Jun 14, 2019 1:43 PM

Hello Ben,

My name is Sabina and I will be assisting you. In order to provide a more accurate solution I will need more information. I would like to confirm first if the NXP device you are using is in fact the LPC824.

1. Are you using any of the examples we provide?

2. Can you specify the communication protocol that your radio device supports? I ask this, because it seems strange that if the radio device supports I2C that it does not have an address associated.

Let me know this information, so I can continue to help you.

Thank you and have a great day!

Sabina

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Ben Burch @ Sabina Bruce on Jun 17, 2019 5:45 AM

Sabina,

Well, the object we need to talk with wants to send fixed size 13 byte messages with a function code embedded in a place where it will not serve as a register address. It is NOT a standard i2c part, but is a microprogram using i2c wiring. I am (at the start) using the i2c master polling example which I have modified.

Also in this system, there can be only two devices, either may be master, both have i2c address of 0x00!

What I did discover was;

1. i2c_master_transfer_t structure allows specifying a zero byte register address.

2. Then I2C_MasterTransferBlocking can be used to send the message without the subaddress and without the repeated start step.

So, it appears that I can make it do what I need, but I wonder if this is the best way to accomplish this?

-BenB

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Ben Burch Jun 17, 2019 5:46 AM

Oh, and yes it is an 824. Using the dev board now, but the production part will use the 20 pin package.

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3 Replies

Sabina Bruce Jun 14, 2019 1:43 PM
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Hello Ben,

My name is Sabina and I will be assisting you. In order to provide a more accurate solution I will need more information. I would like to confirm first if the NXP device you are using is in fact the LPC824.

1. Are you using any of the examples we provide?
2. Can you specify the communication protocol that your radio device supports? I ask this, because it seems strange that if the radio device supports I2C that it does not have an address associated.

Let me know this information, so I can continue to help you.
Thank you and have a great day!
Sabina
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- Ben Burch @ Sabina Bruce on Jun 17, 2019 5:45 AM
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  Sabina,
  
  Well, the object we need to talk with wants to send fixed size 13 byte messages with a function code embedded in a place where it will not serve as a register address. It is NOT a standard i2c part, but is a microprogram using i2c wiring. I am (at the start) using the i2c master polling example which I have modified.
  
  Also in this system, there can be only two devices, either may be master, both have i2c address of 0x00!
  
  What I did discover was;
  
  1. i2c_master_transfer_t structure allows specifying a zero byte register address.
  2. Then I2C_MasterTransferBlocking can be used to send the message without the subaddress and without the repeated start step.
  
  So, it appears that I can make it do what I need, but I wonder if this is the best way to accomplish this?
  
  -BenB
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Ben Burch Jun 17, 2019 5:46 AM
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Oh, and yes it is an 824. Using the dev board now, but the production part will use the 20 pin package.
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Can the I2C API be used without a subaddress/register address step?

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