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M2i.60xx / M2i.60xx-exp Manual
External clocking
Clock generation
Due to the fact that the driver needs to know the external fed in frequency for an exact calculation of the sampling rate you must set the
SPC_REFERENCECLOCK register accordingly as shown in the table below. The driver automatically then sets the PLL to achieve the desired
sampling rate. Please be aware that the PLL has some internal limits and not all desired sampling rates may be reached with every reference
clock.
Example of reference clock:
The reference clock must be defined via the SPC_REFERENCECLOCK register prior to defining the sample rate
via the SPC_SAMPLERATE register to allow the driver to calculate the proper clock settings correctly.
Termination of the clock input
If the external connector is used as an input, either for feeding in an external reference clock or for external clocking you can enable a
50 Ohm termination on the board. If the termination is disabled, the impedance is high. Please make sure that your source is capable of
driving that current and that it still fulfills the clock input specification as given in the technical data section.
External clocking
Direct external clock
An external clock can be fed in on the external clock connector of the board. This can be any clock, that matches the specification of the
card. The external clock signal can be used to synchronize the card on a system clock or to feed in an exact matching sampling rate.
The maximum values for the external clock is board dependant and shown in the table below.
Termination of the clock input
If the external connector is used as an input, either for feeding in an external reference clock or for external clocking you can enable a
50 Ohm termination on the board. If the termination is disabled, the impedance is high. Please make sure that your source is capable of
driving that current and that it still fulfills the clock input specification as given in the technical data section.
Minimum external sample rate
The minimum external sample rate can be as low as DC and the maximum sample rate depends on the specific type of board. The maximum
sample rates for your type of board are shown in the tables below.
Register
Value
Direction
Description
SPC_REFERENCECLOCK
20140
read/write
Programs the external reference clock in the range from 1 MHz to 125 MHz.
External sampling rate in Hz as an integer value
You need to set up this register exactly to the frequency of the external fed in clock.
spcm_dwSetParam_i32 (hDrv, SPC_CLOCKMODE, SPC_CM_EXTREFCLOCK); // Set to reference clock mode
spcm_dwSetParam_i32 (hDrv, SPC_REFERENCECLOCK, 10000000); // Reference clock that is fed in is 10 MHz
spcm_dwSetParam_i32 (hDrv, SPC_SAMPLERATE, 25000000); // We want to have 25 MHz as sampling rate
Register
Value
Direction
Description
SPC_CLOCK50OHM
20120
read/write
A „1“ enables the 50 Ohm termination at the external clock connector. Only possible, when using
the external connector as an input.
Register
Value
Direction
Description
SPC_CLOCKMODE
20200
read/write
Defines the used clock mode
SPC_CM_EXTERNAL
8
Enables external clock input for direct sample clock generation
Register
Value
Direction
Description
SPC_CLOCK50OHM
20120
read/write
A „1“ enables the 50 Ohm termination at the external clock connector. Only possible, when using
the external connector as an input.
