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Help ad converter spartan 3an

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Newbie level 6
Dec 8, 2010
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Hi to all .I try for two months to make ad work .I just use my spi controller . My vhdl script is exactly as timing diagrams chapter 9, ug334 . Is there anything that is not metioned in manual that creates problems such as desabling other spi devices..It is not mentioned . i change spi_sck frequency and have different results. why? i just tried to check gain. So , firstly i make amp_cs low and give the same time spi_mosi the 8th bit of gain so on the first rising edge of spi_sck amplifier captures it . and i capture amp_dout also on rising edge of spi_sck and so goes on until capture all bits. The results that i get on leds depend only of frequency . If frequency is greater than 1mhz all leds light , else two leds , five leds depending on frequency ... Also timing diagrams for ltc1407a are different in manual ug334 and manual for the ltc . Spi_sck is '0' at sample points or not? Also for connecting a dc source do i need something else than vina and gnd pin?

If someone could help me ..thank u

for spi you need to set the minimum and maximum speed so you can find the limitation of your interfacing devices , so try to read the spi manual and find the speed............

Hi.thanks for replying. I know the maximum speed . Ltc1407a-1 is 50 MHz and for ltc6912-1 is 10 MHz . Minimum speed is not mentioned . The only thing mentioned is that may have a problem working on maximum speed. When u say spi manual i suppose u mean my spi devices' manuals. I give spi_mosi always '0' , and the result i get for gain is "00010001" . I can't understand it.

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