How compatible is the Aardvark I2C/SPI Host Adapter in SPI Mode with a Microwire device – can we program a Microwire EEPROM?

Question from the Customer:

I am working on a new product that uses a Cypress GX3 USB to Gigabit Ethernet and a Microwire EEPROM. The setup looks like this:

 Setup for Microwire EEPROM with Aardvark I2C/SPI Host Adapter

Can the Aardvark I2C/SPI Host Adapter program this EEPROM? DI and DO on the EEPROM are connected together (like a half-duplex SPI) - is that a problem?

Response from Technical Support:

Thanks for your question!  The Microwire protocol is similar to SPI; the Aardvark I2C/SPI Host Adapter can easily interface with a Microwire device. Regarding the signals, the main difference is the labeling of the IO pins - the signals are compatible.  Don't worry if you experience a variation with the resistor value, that can be addressed with the following suggestion:

IO Pins

If the Aardvark adapter is the SPI master interfacing with a slave Microwire device, connect the pins as follows:

SPI Master Microwire Slave
SCLK SK  (serial clock)
MOSI SI    (serial in)
MISO SO   (serial out)
SS# CS# (chip select)

If the Aardvark adapter is an SPI slave  interfacing with the master Microwire device, connect the pins as follows:

SPI Slave  Microwire Master
SCLK SK  (serial clock)
MOSI SO   (serial out)
MISO SI    (serial in)
SS# CS# (chip select)

Maximum Current
Looking at the circuit, we strongly recommend increasing the value of the series resistor between DO and DI. The maximum current rating of the Aardvark adapter is 10mA. The current design would reach or exceed that threshold.

Additional resources that you may find helpful include the following:

We hope this answers your question. If you have other questions about our host adapters or other Total Phase products, feel free to email us at, or if you already own one of our devices and have a technical question, please submit a request for technical support.