| ??? 02/04/07 02:21 Read: times |
#131958 - TRUE SPI chip? Responding to: ???'s previous message |
A TRUE SPI chip will have a chip select that, if not asserted will put the chip in "pass through" mode. Thus, if you have a chain of TRUE SPI chips and only one CS is asserted, you will have the effect of 'talking to' one chip only. Sound like JTAG chain. On SPI slave chip, usually, DOUT(MISO) is disabled when CS is inactive. So, the data cannot pass through from DIN(MOSI) to DOUT on this chip when CS is inactive. It is a requirement to connect SPI chips in parallel. And parallel connection is more common on SPI than daisy-chained connection. For example, Maxim show a daisy-chaine connection of MAX525s on this datasheet. http://datasheets.maxim-ic.com/en/ds/MAX525.pdf "Figure 7. Daisy-Chaining MAX525s' (p12) In this figure, /CS of all chips are connected together. It is required to activate DOUT. When SPI chip is connected in parallel, /CS selects a single chip, as shown in "Figure 8." on the MAX525 datasheet. Tsuneo |
