PDP11 PeripheralsHbk 1972 - Trailing-Edge

A B C D E F
4 UNIBUS CONN
3 POWER
2 RESERVED
UNIBUS CONN
Figure 2-30 SS 11 Module Layout
2.4.2 DDII-A Peripheral Mounting Panel
Peripherals may be divided into large and small categories based on the size of
the associated interface logic. If the interface logic (including the M105 Address
Selector and the M782 Interrupt Control) can fit into four module slots, then the
associated device is referred to as a small peripheral. The DDll·A peripheral
mounting panel is a pre·wired system unit designed for mounting up to four small
peripheral interfaces. The physical construction of the DDll·A is similar to the
BSll blank mounting panel.
Use of the DDll·A requires specialized logic cards for the actual interface, since
the pin assignments are fixed for the various control and data signals. Examples
of such interfaces are the DRll·A General Interface (M786 module), LPll Printer
Control (M793 module), CRll Card Reader (M829 module), M792 Diode Memory,
and the KLll Teletype Control (M780 module). Customers may design interfaces
to go into a DDll·A by using the W943 module which allows wire·wrapping of the
integrated circuit interconnections.
Figure 2·31 illustrates module allocation within a DDll·A unit. Slot A2 must be
empty because of power cable overhang; slots S2 and S3 are unused. The DDll·A
is wired to permit the installation of four M7820 modules in column F, four M105
modules in column E, and four double·height device interface modules in col·
umns C and D. The unidirectional grant lines are wired to column D, and each device
interface module must include jumper arrangements to allow selection of the
device priority level at the time of installation. Only SR levels are wired to
this column; devices mounted in a DDll·A unit cannot be assigned to the NPR
priority level without rewiring the panel. An additional constraint imposed on the
interface is that each device may be on only one request level, since both inter·
rupts available through one M7820 module are wired in series and must be at the
same priority level.
If the device requires interface logic that occupies more than one full row of space
in the DDll·A, columns C and D of the second row can be used by using wiring
provided between rows 1 and 2 and rows 3 and 4. If this is done, it is no longer
necessary to add another MI05 and M782 module to slots E and F of the second
row.
Additional considerations that must be noted when using a DDl1-A as well as
specific pin number information is covered in subsequent paragraphs.
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