If someone is using SPI with the ADS1278, I would appreaciate your input.
I am trying to use an ADS1278EVM in SPI mode. My goal is to use high resolution mode, in SPI TDM format.
When I do so, the first bit in my 48 bit data chain appears incorrect. I have grounded the positive and negative inputs of both channels. The data following the MSB is always a chain of ones (a small twos completement negative number). However the first bit, the MSB, is sometimes zero. The second channel has a chain of numerous zeros until the LSBs, (consistent with a small positive twos complement number) although the MSB is sometimes 1 (I expect it is really the LSB of channel 1).
Same actual data is as follows. It consist of an array of 8 sets of samples of channel 1 & 2 data. Each word [0] and the 8 msb of word [1] should be one channel, while the 8 LSB of word [1] and the entire word [2] should be the second 24 bit sample. Note each sample, except for the MSB, always begins with a string of ones or zeros.
[0] = 0x0000C000@Data
[0] = 1111111111111111
[1] = 10001110-00000000
[2] = 0000000110011001
[1] = 0x0000C003@Data
[0] = 1111111111111111
[1] = 11100111-10000000
[2] = 0000000110011100
[2] = 0x0000C006@Data
[0] = 1111111111111111
[1] = 01111011-10000000
[2] = 0000001111000111
[3] = 0x0000C009@Data
[0] = 1111111111111111
[1] = 10101111-00000000
[2] = 0000000100100011
[4] = 0x0000C00C@Data
[0] = 1111111111111111
[1] = 11111001-00000000
[2] = 0000000100010011
[5] = 0x0000C00F@Data
[0] = 1111111111111111
[1] = 11110001-00000000
[2] = 0000001001001001
[6] = 0x0000C012@Data
[0] = 1111111111111111
[1] = 11001111-00000000
[2] = 0000000110111001
[7] = 0x0000C015@Data
[0] = 0111111111111111
[1] = 10100111-00000000
[2] = 0000000110110001
The settings for the ADS1278EVM board are as follows:
My ADS1278EVM settings are as follows: SW11.1 = M0 = Off, SW11.2 = M1 = ON, SW11.3 = F0 = ON, SW11.4 = F1 = ON, SW11.5 = F2 = ON, SW11.6 = CLKDIV = 0FF. For SW10, 1 & 2 are on and all other are off. NN1, NP1, NN2, NP2 are all grounded, others float. Channel switches are all toward ADC1278 chip. SW1 set to ON BRD TOUT = 7.87 MHZ At this point, I may have a number of issues with my setup which currently respresents my best assumptions. My assumption is that I am getting data from the channels, because the first couple bytes of data are generally all ones or zeros except for the MSB. This is consistent with very small negative and positive twos complement numbers which is what I would expect with shorted inputs. John
