|
|
The PDP-8/I Minicomputer
The PDP-8/I was the first TTL version of the PDP-8 series.
The schematics and engineering drawings I have date back to 1967 -- just when
integrated circuits were coming into "popular" use.
The machine consists of several hundred Flip-Chips -- small, general-purpose
printed circuit boards, with several ICs each, connected to a large backplane.
The backplane was wire-wrapped point-to-point by machine.
A big manufacturing location for PDP-8/I backplanes was right down the street
from me, at DEC's Herzberg Road plant in Kanata, Ontario.
This PDP-8/I came from Mississippi, and is now (2003 12 18)
restored (read more).
I just played chess on it (2003 12 18)!
|
The Front Panel
S
M
L
XL
The PDP-8/I front panel is very impressive -- it displays just about everything that's
happening inside of the machine -- from the current address being executed, the data
in memory, the contents of the accumulator, and multiplier-quotient register to the
decoded instruction being executed and the current state.
|
The Backplane
S
M
L
XL
This is the backplane for the PDP-8/I.
It consists of 8 rows of 40 columns; a large number of which are filled
with the Flip-Chip cards.
|
The Cards
S
M
L
XL
This is the reverse side of the backplane, with around two hundred cards installed.
The purple cards are known as M-series ("M" for Magenta) cards, and contain general-purpose logic, such as 6 flip-flops per card,
or a bunch of NAND gates.
They are constructed from 74-series TTL chips for the most part.
The green cards are known as G-series cards, and generally contain analog functions, such as
the amplifiers for the core memory.
White cards are interface cards, and generally contain little logic, mainly just connectors to
go from one bus to another.
|
S
M
L
XL
This is an annotated diagram, showing the functional groupings of the various cards.
The real beauty of the PDP-8/I is that you can not only look at the schematic and get
a good idea of what's going on, but you can physically find and touch various components.
For example, the six cards at the bottom left, labelled "Major Registers", are where the
flip-flops are that store the accumulator, the program counter, memory buffer, and memory
address. There are two bits per card (2 x 6 = 12 bits).
|
|
|
