Reference Manual

Turbo PMAC/PMAC2 Software Reference

Turbo PMAC Global I-Variables 218

To determine the clock frequencies set by a given value of I7m03, use the following procedure:

1. Divide I7m03 by 512 and round down to the nearest integer. This value N1 is the ADC_CLK divider.

2. Multiply N1 by 512 and subtract the product from I7m03 to get I7m03'. Divide I7m03' by 64 and

round down to the nearest integer. This value N2 is the DAC_CLK divider.

3. Multiply N2 by 64 and subtract the product from I7m03' to get I7m03''. Divide I7m03'' by 8 and

round down to the nearest integer. This value N3 is the PFM_CLK divider.

4. Multiply N3 by 8 and subtract the product from I7m03''. The resulting value N4 is the SCLK divider.

For accessory boards in which alternate addressing of the Servo IC is used (labeled Servo IC m*), this

function is controlled by I7m53, not I7m03.

Examples:

The maximum encoder count frequency in the application is 800 kHz, so the 1.2288 MHz SCLK

frequency is chosen. A pulse train up to 500 kHz needs to be generated, so the 2.4576 MHz PFM_CLK

frequency is chosen. The default serial DACs and ADCs provided by Delta Tau are used, so the default

DAC_CLK frequency of 4.9152 MHz and the default ADC_CLK frequency of 2.4576 MHz are chosen.

From the table:

SCLK Divider N: 5

PFM_CLK Divider N: 4

DAC_CLK Divider N: 3

ADC_CLK Divider N: 4

I7m03 = 5 + (8 * 4) + (64 * 3) + (512 * 4) = 5 + 32 + 192 + 2048 = 2277

I7m03 has been set to 3429. What clock frequencies does this set?

N1 = INT (3429/512) = 6 ADC_CLK = 611.44 kHz

I7m03' = 3429 - (512*6) = 357

N2 = INT (357/64) = 5 DAC_CLK = 1.2288 MHz

I7m03'' = 357 - (64*5) = 37

N3 = INT (37/8) = 4 PFM_CLK = 2.4576 MHz

N4 = 37 - (8*4) = 5 SCLK = 1.2288 MHz