External clocking | Clock generation |
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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 sample rate.
Register | Value | Direction | Description |
SPC_EXTERNALCLOCK | 20100 | read/write | Enables the external clock input. If external clock input is disabled, internal clock will be used. |
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.
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 |
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Minimum external sample rate
The minimum external sample rate is limited on all boards to 1 kHz 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.
Maximum external samplerate in MS/s
Remapped channels |
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| 3110 | 3111 | 3112 | 3120 | 3121 | 3122 | 3130 | 3131 | 3132 | 3140 | |||
ch0 | ch1 | ch2 | ch3 | ch4 | ch5 | ch6 | ch7 | ||||||||||
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| 1 | 1 | 1 | 10 | 10 | 10 | 25 | 25 | 25 | 50 |
x | x |
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| 1 | 1 | 1 | 10 | 10 | 10 | 25 | 25 | 25 | 25 |
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| n.a. | n.a. | 1 | n.a. | n.a. | 10 | n.a. | n.a. | 25 | n.a. |
x | x |
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| n.a. | n.a. | 1 | n.a. | n.a. | 10 | n.a. | n.a. | 25 | n.a. |
x | x | x | x |
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| n.a. | 1 | 1 | n.a. | 10 | 10 | n.a. | 25 | 25 | n.a. |
x | x | x | x | x | x | x | x | n.a. | n.a. | 1 | n.a. | n.a. | 10 | n.a. | n.a. | 25 | n.a. |
An external sample rate above the mentioned maximum can cause damage to the board.
Ranges for external sample rate
Due to the internal structure of the board it is essential to know for the driver in which clock range the external clock is operating. The external range register must be set according to the clock that is fed in externally.
Register | Value | Direction | Description | |
SPC_EXTERNRANGE | 20130 | r/w | Defines the range of the actual fed in external clock. Use one of the below mentioned ranges | |
| EXRANGE_SINGLE | 2 | External Range Single | |
| EXRANGE_BURST_S | 4 | External Range Burst S | |
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| EXRANGE_BURST_M | 8 | External Range Burst M | |
| EXRANGE_BURST_L | 16 | External Range Burst X | |
| EXRANGE_BURST_XL | 32 | External Range Burst XL | |
The range must not be left by more than 5 % when the board is running. Remember that the ranges depend on the activated channels as well, so a different board setup for external clocking must always include the related clock ranges.
This table below shows the ranges that are defined by the different range registers mentioned above. The range depends on the activated channels and the mode the board is used in. Please be sure to select the correct range. Otherwise it is possible that the board will not run properly.
60 | MC.31xx Manual |
