How critical is the bitrate setting in SPI Slave mode? Does the Aardvark I2C/SPI Host Adapter communicate only with other SPI devices that support exactly the clock speeds that the Aardvark does? If not, should the bit rate on the Aardvark be configured higher than that of the SPI master or lower?

Also, the Control Center Serial Software User Manual uses terminology such as rising/falling and sample/setup. How do those terms correlate to CPOL (clock polarity) and CPHA (clock phase), and can you provide more information about that configuration?

Thanks for your questions! Setting the bitrate applies only to the device in the SPI master mode; it is not necessary to set the bitrate for the device in slave mode, as SPI slave devices use the clock of the master. However, the master and slave devices must agree to the data frame, which is related to the clock transitions, polarity and phase, as indicated in section 4.2 of the Control Center Serial Software User Manual.

Figure 1: Configure SPI Mode via the Control Center Software Serial

The Aardvark adapter is capable of sending SPI data at 8 MHz, while our newest product, the Promira^™ Serial Platform, with the SPI Active – Level 1 Application, can send data at 12.5 MHz. The Control Center Serial Software can be used with both devices.

Here are the definitions of rising/falling and sample/setup, relative to CPOL and CPHA:

• rising/falling is equivalent to CPOL = 0; the leading edge of the clock is rising and the trailing edge is falling.
• falling/rising is equivalent to CPOL = 1; the leading edge of the clock is falling and the trailing edge is rising.
• sample/setup is equivalent to CPHA = 0; data is sampled on the leading edge of the clock.
• setup/sample is equivalent to CPHA = 1; data is sampled on the trailing edge of the clock.

Based on those settings, four SPI modes are possible, which are illustrated in Figure 2 below.

Figure 2: Clock Polarities and Clock Phases of SPI Modes