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How Many I2C GPIOs are Available, and What Is the Effect of the Promira Serial Platform Pull-Up Resistors?
Rena Ayeras

Question from the Customer:

I am designing a PCB for a new project. I am considering the Promira Serial Platform for speed, I2C protocol support, as well as connecting to a target board for development. I have looked at the Promira Serial Platform datasheet, and I have some questions:

  • Which GPIOs are available with the applications I2C Active - Level 1 Application and I2C Active - Level 2 Application?
  • Will pull-up resistors be needed for the GPIO pins?
  • What are the physical dimensions (or connector standard) for connecting the Promira Serial Platform device to a target board?
  • About the target board – to become familiar with the I2C protocol at 1 MHz and 3.4 MHz, which of your accessory boards do you recommend?

Response from Technical Support:

Thanks for your questions! The Promira Serial Platform and the available applications make this device very flexible and capable of fulfilling many needs. We are providing the requested information in the following sections.

GPIO Signals

Here is information that applies to both I2C Active Level 1 and Level 2:

  • MOSI, SCLK, and MISO pins are not available as GPIO signals.
  • All six SS signals (which are used for SPI protocols) are available as I2C GPIO signals.
  • Specific pins designated as GPIO signals.

The total number of available GPIO signals depends on which level of I2C application is being used, which are listed in the following sections. For more information about the pinout, please refer to the Hardware Specifications section of the Promira Serial Platform I2C/SPI Active User Manual


Available GPIO Signals for I2C Active – Level 1 Application

With the I2C Level 1 application, up to 10 GPIOs are available. The pinout is listed below:

  • GPI00: Pin 1
  • GPI001: Pin 3
  • GPIO02: Pin 9
  • GPIO03: Pin 14
  • GPIO04; Pin 15
  • GPIO05: Pin 17
  • GPIO06: Pin 19
  • GPIO07: Pin 20
  • GPIO08: Pin 26
  • GPIO09: Pin 21

GPIO Signals for I2C Active – Level 2 Application

Note  – to use the  I2C Active - Level 2 Application, which supports speeds up to 3.4 MHz, the Level 1 application that supports up to 1 MHz must be previously installed.

With the I2C Level 2 application, up to 16 GPIOs are available. The I2C GPIO pinout is listed below:

  • GPI00: Pin 1
  • GPI001: Pin 3
  • GPIO02: Pin 9
  • GPIO03: Pin 14
  • GPIO04; Pin 15
  • GPIO05: Pin 17
  • GPIO06: Pin 19
  • GPIO07: Pin 20
  • GPIO08: Pin 26
  • GPIO09: Pin 21
  • GPIO10: Pin 23
  • GPIO11: Pin 25
  • GPIO12: Pin 27
  • GPIO13: Pin 31
  • GPIO14: Pin 32
  • GPIO15: Pin 33

GPIO Internal Pull-Up Resistors

The Promira platform pins are open drain and have internal pull-up resistors. The values of internal pull-ups for the GPIOs of the Promira platform are listed below:

  • GPIO00 / GPIO01 signal pull-ups are 560-ohm resistors.
  • GPIOs 02, 03, 04, 05, 06, 07, 08, 15 have stronger pull-ups – the signals from power up and beyond have 2.2K ohm pull-up resistors.
  • GPIOs 13, 14 signals from power up and beyond have 1.5K ohm pull-up resistors.
  • GPIOs 09, 10, 11, 12 signals have weak pull-up resistors.

Effects of Internal 560 Ohm Resistors for GPIO00 and GPIO01

Because of the 560-ohm resistors, there are factors to consider when using the signals GPIO00 and GPIO01.

When the Promira platform is connected to Control Center Serial Software, configured for GPIO input, and the target device does not drive the Promira platform, GPIO00 reads 1 (logic high).

  • In this case, the GPIO00 pull-up resistor creates the logical 1.
  • Enabling or disabling the I2C signal pull-up does not affect the GPIO00 and GPIO01 signals. The GPIO00 and GPIO01 signals always have an active pull-up, which is a separate resistor from the I2C signal pull-up resistor.

When the Promira platform is connected to Control Center Serial Software and configured to GPIO input, we recommend having the target device drive the Promira platform.  This ensures the GPIO00 and GPIO01 signals are read correctly.

  • The Promira platform GPIO00 / GPIO01 signal pull-up value is 560 ohms and cannot be configured (enabled/disabled).

Test and Development

For initial tests and development, as well as troubleshooting, we recommend the I2C/SPI Activity Board.  This target board includes an I2C EEPROM: AT24C02 256 Bytes/22 Kilobit (8-byte pages) 2-Wire Bus Serial EEPROM (Atmel).

Promira Signal Connector

The 34-pin to 34-pin connectors on the Promira platform’s 34-Pin: 34-Pin header cable uses a standard ribbon cable and a 2x17 IDC female connector.

  • The cable is 0.039″ (1 mm) pitch that is 5.12″ (130mm) long
  • The 2x17 IDC female connector is 2x2mm (0.079x0.079). The IDT ribbon connector has polarizing key and locking ramps, is available as Molex 0875683493.

The following connectors are compatible:

We hope this answers your questions. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application.