05-21-2017, 05:13 AM
(This post was last modified: 05-21-2017, 08:11 AM by MarkHaysHarris777.)
(05-20-2017, 09:33 PM)MarkHaysHarris777 Wrote: Use multiplexing;
... the 74hc165 is a parallel in serial out chip; you multiplex and latch the ADC of choice and then use SPI to bring the ADC bits into the pine via serial. The 74hc595 reverses that. A combination of 165 and 595 is generally used to scan a keyboard matrix, for instance.
Basically each ADC has its own parallel to serial setup. Your software should use multiplexing to select the parallel to serial setup (for the particular ADC) and then SPI is used to read it. This can be done with i2c as well.
Heck yeah your pine and SPI can keep up with your ADC chips;
How many bps can SPI do on the pine? What clock rate is a SPI channel clocked at??? The processor frequency or the external oscillator freq?
I know the main processor is at 1100 mhz, which would be plenty given SPI's single bit per cycle, but does the SPI run at that clock rate?
800K 8 bit samples is 6.4megabits per second for 1 a/d channel, with framing bits say 8 megabits/channel
with 4 channels its 32 megabits/channel, which would need a 32 mhz clock rate on a SPI bus...within spi specs of 20-100 mbps, but I start to worry about the 74165, its specs say 28mhz top freq, could 2 74165's do 2 spi channels?
Perhaps just keeping the circuit simple even if it needs 8*4=32+8(control) 40 gpio signals? Though its a lot of wiring...
Thanks!
E