> Interesting... 5Mbaud over RS232 pins? > I didn't think RS232 could allow for such speeds... given > the hazards of crosstalk, etc.
The pins are the same, no matter if they are configured as SPI or USART. (I2C can be different, e.g. limited slew rate). The usualy given maximum speed for RS232 thinks of +/-12V levels, plugs, and cabling outside a device. There are limits, and I wouldn't try more than 115kBaud then. But if the signals stay on one PCB, there is no real difference between USART and SPI regarding transmission speed. > The daisy-chain setup is quite useful in a serial bus... > what's the theoretical limit with PIC SPI? > 128 devices per bus? or is it higher than that? Daisy-chain is not really a bus. There is no limit when daisy-chaining. The single devices do not know that they are daisy-chained, it is the software's job to find out which byte shall be used by a single device, and which is only passing through. When wiring as a bus, there are several soft limits: Electrically, how many inputs can one output drive? Can be increased by buffers. Logically, how mand CS-lines can I provide? Can be increased by port expanders, shift registers, latches, line decoders or counters. In other words: There is also no hard limit. Hard limits only exist in busses that have a mandatory device numbering like I2C. > only used 16 data pins, and 5 control lines! To add a > second "bus"... all you'd need is another 5 control pins > (if you need all 5 separate), which is very easy given the > left over real-estate of the original schematic. I don't quite remember the control lines... You are right, if you can set both the Master and the Slave drive bus outputs to HI-Z using the control pins, you can easily add more drives. But then, there's no reason to say it was impossible to use more than four. Greets, Kiste -- You received this message because you are subscribed to the Google Groups "jallib" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/jallib?hl=en.
