PCSAT2 COMMAND/CONTROL FUNCTIONS                       5 April 2003
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                                                             WB4APR

PCsat2 Command and Control functions are provided through the two
dual redundant (COTS) Terminal Node Controllers.  Each controller
has a 9600 baud serial port, 10 ON/OFF command bits (switches) and
five 0-5 volt analog telemetry channels.

SERIAL PORTS:  The serial ports are available for communications
with the solar power experiment processor.

COMMAND SWITCHES:  In general most of these 10 command switches are 
open collectors wired in parallel so that either TNC can command the 
function.  The ones that are only available on one side or another
are marked with an asterix (*).  Applications of these 10 switches 
are as follows:

TNC-A COMMAND  TNC-A DESCRIPTION      
-------------  -----------------------------------------------
CTRL A ON:     Reset 8 Hour EVA timer 
CTRL B ON:     Toggle Solar-EXperiment power

OUT 01111111:  Toggle the 96 hour failsafe restart line
OUT 10111111:  *Reset other TNC
OUT 11011111:  Activate RX heaters (1W at 0 deg C)
OUT 11101111:  Activate VHF transmitter
OUT 11110111:  Toggle Charge Rate A/B line
OUT 11111011:  *Enable PSK-31 or Repeater for user access
OUT 11111101:  *Backup override enable PSK-31 or Repeater
OUT 11111110:  *Complementary backupoverride bit

FAULT-TOLERANT DESIGN:  The DEFAULT, RESET, LOW POWER and FAILSAFE 
mode for all of these outputs are OFF, or no effect.  Notice the
complementary bits for the REPEATER and PSK-31 Backup Override
functions.  This assures that a dead TNC or locked-up TNC cannot 
permanently leave these devices on because they must have mirror 
image bits to activate.

Bob Bruninga
USNA Satellite Lab 
      
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