I have a project where I need to log both transmit and receive data to and from a cellular modem module. The data will be collected from a remote location over a period of a couple of weeks. I picked up a couple of open log boards, a DS3234 RTC board and a basic FTDI board from Sparkfun and a couple of 4GB microSD cards. I've modified the open log firmware so that the master open log board will read the time and date from the RTC using software SPI and then use the manchester library to send the time over to the slave open log board using a single wire. Each slave open log board will send the time to the next slave in the chain. To do this, PC0 is used to send the data downstream and PC1 is used to receive the data from upstream. The time is read by the master and propagated to the slaves just after power-up of the logger. I then count on each logger to periodically write the time/date to its log file. This time entry is made prior to the open log firmware entering sleep state which happens when no data is received for 2 seconds. The basic FTDI board is only used to program each of the open logger boards.
I'll post links to the various Arduino libraries that I've modified once I get caught up here a bit.
Enjoying life in Canada!