ITU G2 Special Modes

The ITU currently supports two special modes for communication with data loggers. Data loggers are frequently operated off batteries and therefore power saving is important. A significant power saving can be achieved by sleeping the serial ports. This does, however, introduce a requirement to wake up the unit when needed and to allow it to return to its sleep mode afterwards. The procedures for this differ with the different loggers.

Note that normal mode corresponds to AT^HSPM=0. The show all settings command only shows the special mode setting if it is in other than normal mode.

Campbell Scientific Inc. (CR10X)

AT^HSPM=1

The Campbell logger uses two signals for its wakeup handshaking. These they call RING (Ring Indicator) and ME (Modem Enable). To wake up the logger it is necessary to take the RING input high (5V) until the logger responds by taking ME high (5V). The RING input can then be taken low (0V) again so that the logger can go back to sleep mode again. This happens after a timeout period (60s) or when given an appropiate command. The logger keeps ME high as long as it's awake.

The ITU takes RING (ITU: RI) low (logic 1) whenever it receives a data packet. It keeps it low only until it sees the ME line (ITU: RTS) go high (logic 0) then it returns it to high (logic 0). The only other special thing that the ITU does for the Campbell is to ignore the state of RTS and treat it as always true from the point of view of it being RTS.

Unidata Australia (Starlogger)

AT^HSPM=2

To power up the Starlogger it is necessary to take its RTS input positive. It then takes around 15-20ms to actually wake up, after which time it responds by taking its DSR line positive. The logger will go straight back to sleep if RTS is not kept positive. After a timeout period (20s) or upon processing a kill command ('K') the Starlogger will return to sleep mode. All of the Starloggers RS-232 drivers are switched off in sleep mode.

When the ITU receives a packet in Unidata mode it asserts RTS (ITU: RI) (positive, logic 0). It then wait 25ms before starting to send the received data to the logger. This is to allow the logger time to wake up. During testing wakeup times were observed to be in the range of 15-20ms. The ITU then keeps RTS (ITU: RI) asserted until it sees DSR (ITU: RTS) go low. The Starlogger takes DSR (ITU: RTS) low (turns off the driver in fact) when it goes back to sleep. The ITU then needs to take its RTS low to stop it waking up again. The ITU has a 60s timer and will take RTS (ITU: RI) low when this timer expires even if it hasn't seen DSR (ITU: RTS) go low yet. Like with the Campbell mode, the ITU ignores the state of its RTS and treats it as always true from the point of view of it being RTS.