I have the following questions:
- For DS1302 real time clock, there is an option to connect a backup power source to Vcc1. However, I'm not too sure what source that I should be using, but I'm thinking something along the lines of a watch battery. Any suggestions would be very helpful.
- For the PIC18F2620 MSSP module, if I want to control devices in SPI mode, is it by default that I can only control one device by SPI with that microcontroller? I know that I can only communicate to one device at a time b/c I only have one module, but would it be appropriate if I have a few unused I/O pins to be used as addressing outputs to a decoder to have the decoder's output be used as Chip Enable for setting which device I want to communicate to? Also, would I cause any damage to a SD card or real time clock chip if I have data streaming into or out of the slave devices when the chip enable for that particular slave device isn't set to high?
- In the event where I can't easily communicate to multiple devices through SPI on a single microcontroller system, how hard would it be to write data on the unused memory of the microcontroller?
Thanks for your time in terms of looking into the questions.