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Nine-wire Bus Specification

The table below is a tidied-up version of Cliff's original thoughts on the bus. You can view these here.

10 Pin Header Label Function
1 AW Arbitration wire controlled by sensor driver modules to facilitate shared access to the TTL serial line.
2 Tx0 to device RS232 serial receive line usually for console use.
3 Rx0 from device RS232 serial transmission usually for console use.
4 +V Unregulated +V DC power supply (7 to 17 volts). Regulated supplies are generated from this line using voltage converters/regulators as appropriate for each device
5 Gnd Ground at 0 volts.
6 Spare N/A
7 Tx2 to device Shared TTL serial data request transmission line to sensor modules.
8 Rx1 from device RS232 serial receive line from device to Bitsy eg NMEA.
9 Tx1 to device RS232 serial transmit line from Bitsy to device eg dGPS.
10 Rx2 from device Shared TTL serial data receive line from sensor modules.

NOTE: the colouring scheme given above only works if the 10 pin headers are clipped onto the bus with the triangle/arrow situated on the same side as the black wire (making it pin 1).

In the current environment, the serial lines are dedicated as such:

Serial Line Bitsy Device Function
0 /dev/ttySA0 Console
1 /dev/ttySA1 RS232 Device eg GPS.
2 /dev/ttySA2 TTL Sensor Devices, such as compasses and accelerometers.

Device Connector

To complete the picture the figure below shows the bus connector used on the sensor devices. Note that the numbering scheme is Chris's and does NOT correspond with the moulded numbers on the connector.

Note also that the picture of a bus socket below is the device point of view, hence the Tx up above is an Rx here and vv.

Spare Rx2 from host Tx1 to host Rx1 from host Tx2 to host
6 7 8 9 10
1 2 3 4 5
Req Rx0 from host Tx0 to host Vcc Gnd

This page last updated July 7, 2003
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