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32 71/2 CONTROL UNIT TO DEVICE INTERFACE
The 3271/2 Control unit (i.e., 3271 Mod 1, 2, 11, 12, or
3272 Mod 1 and 2) to Device (i.e., 3277 Mod 1, 2; 3284/6
/^ Mod 1, 2; or 328 8 Mod 2) interface is a single wire coaxial
cable interface (RG62AU Coax, Characteristic Impedance 9 3
Ohms) with serial by bit data transferred in either direction
but only one direction at a time. The Control Unit operates
as a master and the attached device as a slave. Each
device, attached directly to the Control Unit, receives
and sends data addressed to that device only.
Bits on the coax appear as negative-going pulses. The
center conductor of the coax, when measured at the Con-
t r o l Unit with reference to the outer conductor (shield),
w i l l be +7.4 v o l t s nominal (5.2v min, 8.5v max) with no
signal present and power on at each unit. For maximum
coax cable length (2000 feet) the signal from the Control
Unit on the coax w i l l appear as follows at the device:
BITS 1 thru 10 BITS 11 and 12 BIT 13
1.050us + 20ns 1 . 2 6 0 u s + 20ns 1.470us + 20ns
TV
! X\
2.4V
Min