ADLINK Technology NuDAQ PCI-9812/10, Руководство пользователя

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Registers Format
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23
4.11 Clock Source Register
The register is used to select the system clock source.
Address: BASE + 20h
Attribute: write only
Data Format:
Bit 7 6 5 4 3 2 1 0
BASE+18h --- --- --- --- --- CLKSRC1 CLKSRC0 Freq_Sel
BASE+19h --- --- --- --- --- --- --- ---
BASE+1Ah --- --- --- --- --- --- --- ---
BASE+1Bh --- --- --- --- --- --- --- ---
bit 31..3 -- don't care
bit 2..1 -- CLKSRC1..0, ADC clock source
bit 0: --- Freq_Sel, Frequency selection.
Freq_Sel : 1: frequency of A/D clock source is higher than PCI
clock frequency (33 MHz)
0: frequency of A/D clock source is lower than PCI
clock frequency (33 MHz)
CLKSRC2 CLKSRC1 selected clock source
0 0 internal clock (40 MHz)
0 1 external sine wave clock
1 0 external digital clock
1 1 illegal
Note: When external clock is selected, this external clock is also
divided by the frequency divider as mentioned before, so the
frequency of the external clock should be at least twice as the
desired sampling frequency.