Q: We are using an Aardvark I2C/SPI Host Adapter in our test setup to read a GPIO pin and act as an SPI Master.  I observed there is a delay of approx. 7μs between bytes in the SPI transfer.  This delay seems to be present when I use the Control Center Software to drive the device, and also when I use the API functions to configure the device.  Is this a fundamental limitation of the device?  Ideally we would like to perform full duplex SPI transfers of up to 40 bytes at 4MHz with no inter-byte gaps.

A: Thanks for your question! The Aardvark I2C/SPI Host Adapter is a general purpose device that can actively communicate on the bus, and provides master and slave capability as well as SPI and I2C features. Regarding your question, the timing specifications are described in section 2.4 of the Aardvark I2C/SPI Host Adapter data sheet.

Figure 1: Aardvark Host Adapter SPI Byte Timing

As an SPI Master, the Aardvark I2C/SPI Host Adapter can operate at bitrates of 125 kHz, 250 kHz, 500 kHz, 1 MHz, 2 MHz, 4 MHz, and 8 MHz. As an SPI Master, the range of the setup time (td) between bytes is 7 μs to 9 μs. This timing feature is fixed; it cannot be adjusted.

For your application, we recommend using the Cheetah SPI Host Adapter, which is specifically designed to communicate at high speed with SPI-based systems. As an SPI Master, the Cheetah SPI Host Adapter actively communicates on the bus, operates at higher speeds (up to 40+ MHz), can provide gapless shifting, and provides more control over the timing of the data that is shifted out.  Timing specifications are shown in Section 2.5 of the Cheetah SPI Host Adapter Data Sheet.

Figure 2: Cheetah SPI Host Adapter SPI Byte Timing

The minimum setup time of the Cheetah SPI Host Adapter is 4.8 ns, which is much less than the minimum setup time of the Aardvark I2C/SPI Host Adapter (7 μs).  The Cheetah SPI Host Adapter does not read GPIO.

For more details and for comparing devices, please refer to the following documents:

Product Selector Guide

Aardvark I2C/SPI Host Adapter

Aardvark I2C/SPI Host Adapter datasheet

Control Center Software

Cheetah SPI Host Adapter

Cheetah SPI Host Adapter datasheet

Cheetah GUI Software

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 sales@totalphase.com or support@totalphase.com.