clock question

Steve Andrues

I·currently have a project running a Dallas Semi DS1302 RTC.· Now that I have all of the timekeeping issues fixed I wish to add an ADC to the project.· The ADC I want to use is the MCP3208.· The DS1302 already has a pin defined as Clock.· Is there any reason why I cannot use this same pin to drive the clock on the ADC?· Uncommitted pins in this project are getting to be sparse.
Any help will be greatly appreciated.

Mike Green

Both the DS1302 and the MCP3208 use what's known as an SPI interface. This tends to vary a lot from device to device, but, at its heart, there's a chip select which has to be unique for each chip. There's a clock line which can be shared among chips. There's also one (in the DS1302) or two (in the MCP3208) data line(s). I'd connect the single I/O pin from the DS1302 to the Din line of the MCP3208. The Stamp will use 3 I/O pins (for Clock, Din, and Dout) plus two chip select pins (one for each). I'm not sure if you can share one I/O line for the MCP3208's Din and Dout lines. I'd need to go through the datasheet very carefully to make sure Dout is a high impedance when Din is being used.