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Table 7-39 GBUS$SERNUM Register Bit Definitions (Continued)
Name
Bit(s)
<4:3>
EXPSEL
<2>
XMT_DATA
<1>
RCV_DATA
<0>
SROM_CLK
7-84 System Registers
Type
Function
R/W, 0
Expander Select. Selects which cabinet the
power supply UART lines are logically connected to
and, therefore, which set of three 48V power sup-
plies are connected to the PS lines. May be used by
console when TLDIAG<FRIGN> is set for commu-
nication between the CPUs.
EXPSEL
00
01
10
11
Transmit Data. This bit must be set to receive
W, 1
data from RCV_DATA.
Receive Data.
R, 1
Serial ROM Clock.
W, 1
Selection
PS lines talk to the main CPU
cabinet.
PS lines talk to the right ex-
pander cabinet.
PS lines talk to the left ex-
pander cabinet.
PS transmit line is looped back
to PS receive line.
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