Digital Equipment MicroPDP-11 Technical Manual page 29

BA23 Enclosure
The signal distribution panel carries the signals from an RQDX controller module
installed in the Q22-Bus backplane. Six connectors on the signal distribution panel
provide the following functions:
• J6 Removable Disk 1+2 - provides the signals to an RX50 diskette drive. An
RX50 diskette drive contains two disk units. When a fixed disk drive is present,
the ROM code usually labels these as disk unit 1 (DUl) and disk unit 2 (DU2).
• J7
Fixed Disk 0 and J2 Fixed Disk 0 - provide the signals to a fixed disk drive
installed in port 0 (left slot) of the BA23-A enclosure. This is the first fixed disk
drive to be booted, and the ROM code usually labels it as disk unit 0 (DUO).
• Jl
Fixed Disk 1 and J5 Fixed Disk 1 - provide the signals to a fixed disk drive
installed in port 1 (right slot) of the BA23-A enclosure. This is the second fixed
disk drive to be booted, and the ROM code usually labels it as disk unit 1
(DUl).
CAUTION
Never install more that one fixed disk drive in a BA23-A enclo-
sure. Damage to the system could result.
• J4 - provides the signals to the control panel printed circuit (PC) board from the
mass storage signal distribution panel.
A TK50 tape drive, installed in the BA23 enclosure, connects directly to its
TQK50 controller module with a ribbon cable. This cable passes through the access
door on the signal distribution panel and under the Q22-Bus backplane.
1.5.2 Q22-Bus Backplane
The backplane implements the extended LSI-11 bus, which uses 22-bit addressing
to support up to 4 megabytes of main memory. This bus is commonly referred to
as the Q22-Bus.
The Q22-Bus backplane supports a maximum of 38 ac loads and 20 dc loads. The
ac loading is the amount of capacitance a module presents to a bus signal line; one
ac load equals 9.35 picofarads (pF). The dc loading is the amount of dc leakage a
module presents to a bus signal line; one dc load is approximately 105
microamperes
(J.lA).
The backplane itself presents 7 ac loads and no dc loads.
Four connectors on side 2 of the backplane (Figures 1-7 and 1-8) provide the
following functions:
• ]1 -
provides the connection for the power supply backplane cable which carries
the dc power and signals from the power supply.
• J2 - provides the signals to the control panel printed circuit board from an
installed CPU module.
• J3 and
]4 -
provide for termination of the mass storage power cable when no
mass storage device is present.
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