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PDP-11/70 'in-a-box' | |
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| mounting bracket and "L-profile" | 11/70 panel, bracket and "L-profile" | panel corner with bottom plate |
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The bracket has two 90° edges. The slanted edge is mounted against the rear of the front panel, the straight edge is mounted onto the
bottom plate (with the L-profile edge in between). To fit the L-profile, the end at the panel side must be cut a little. On the picture
at the right you can see how the bottom plate hides behind the rim of the front panel, and how the L-profile and the bracket are mounted.
Between the L-profile outer side and the vertical rim of the front panel is 2 mm space: exactly the room to install the side plates.
Practical tip: keep the "L-profile" strips a bit too long. When you put all together, you can cut off the excess of length.
Bottom and chassis
Just like the bottom plate, the side panels move behind the sides of the 11/70 console frame. I first cut the shape of the panels
out of cardboard, before I made them in aluminum. Then I drilled the mounting holes and made the L-shaped edges to mount the panels.
As I figured that it would be handy to have a 3½" floppy disk drive installed (for the built-in PC), I made an opening in the panel
at the right side, and cut a rectangle out of the bracket that holds the 11/70 console. Using 3 pieces of L-shaped aluminum I mounted
the floppy drive on this bracket. A small bracket fixes the outer right side panel with the bracket to make the whole construction
more sturdy, as you will be pushing the floppy disk eject button!
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Power supply installation
The modern PC power supplies do not have many holes to install it in a hobby enclosure, and require that some sides do not
block the flow of (cool) air. To mount the supply I decided to split the rear panel into two pieces. The bottom piece is
made of a strip of steel that has many small openings.
PC installation and connections
When the hard disk, the floppy disk drive and the power supply are installed, it is time to install the single-board PC.
Make all the necessary connections, for now that are the following.
Install the I/O Board. Connect the +5V. and Gnd pins of the Core Board to the PC power supply. Connect the other end of the
flat cable from the Core-I/O header on the Core Board to the Core-I/O header on the I/O Board. Make sure pin #1 aligns.
This wiring is not complex.
I/O Board to PDP-11/70 console connection
This is where most of the electrical work is ...
All LEDs, switches etc. on the PDP-11/70 console are connected to three 40-pin ribbon cables with IDC headers. The input
ports and output ports on the I/O board are grouped per 2 ports on a 16-pin header. So, I needed some sort of
"interconnection" board to make the transistion from the I/O headers to the headers on the PDP-11/70 console board.
First, I defined the allocation of the input ports and output ports to the LEDs, switches etc. in the Core Board firmware.
I have done that and made a new firmware EPROM, which also contains a few more interface functions that can be called to
control the LEDs in an efficient way (read: less message bytes from SIMH to the Core Board, thus improving performance).
The following table shows the allocation.
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When all connections are defined you know on which pin of which INport or OUTport header a switch or LED must be connected.
The PDP-11/70 console panel has four connectors, and you need them all four. One is the 8-pin Molex connector for
the power supply of the LEDs and (most of) the logic on the console board, the other three are BERG connectors through
which all switches and LEDs are connected to the I/O Board.
(Right-)click the following link to get a copy of the
PDF file description of the 11/70 console board (5 pages, 507 kb) from the bitsaver's mirror site. I will refer to these pages a bit further down this page.
You see the three 40-pin connectors, named J1, J2, and J3. The pins on these connector are named as follows.
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How (which order/sequence) you connect the connector pins to the I/O Board is not particular important as you assign the
output port bits in the software. However, it is clever to allocate the Address and Data Switches and LEDs in the proper
sequence, that is bit 0 = D0, bit 1 = D1, etc. If you connect everything as I show on this page, you can ask me for the
modified firmware.
The text in orange boxes are outputs (LEDs), the text in green boxes are inputs (switches/toggles) for the I/O Board,
text in white boxes is power supply, and the text in grey boxes is not connected or not used.
The picture shows how I built the interconnection board. The blue 6-screw connector is wired to the 8-pin Molex connector
J4 of the console, and the 4-screw connector is the connection to the PC power supply (+5 Volt, Gnd, and the two
connection to activate the ATX power supply via the console key switch!) The 4-pins marked "+" and "-" are the
power supply connections to the Core and I/O Board.
If the interconnection board dimensions are 100 x 160 mm ("Euro card" size), you can mount the I/O Board on top of the
interconnection board with hexagonal stand-offs. The "holes" in the figure indicate where the I/O Board will be mounted.
The Core Board can be mounted on top of the I/O Board using hexagonal stand-offs. Of course, this depends on how you want
to make your construction. I promised Edward to assemble a Core and I/O Board, and build an interconnection board for
his
If your PDP-11/70 console has the black metal plate at the rear side (used to mount the console on the front of the
processor box), you can also mount the 3 boards (Core, I/O and interconnection) next to each other on the metal plate.
Doing so, all electronics upto the
There is no need for male headers with a shroud, but if you use headers with a shroud check the "opening" at one long
side of it. That is the side where the odd-numbered pins are. As you can see from the pictures I did that not entirely
correct. It is not really an issue, as long as you make sure that pin #1 at one end of the ribbon cable matches on the
boards with pin #1 at the other end (or solder the interconnection board wiring between the 16-pin headers and 40-pin
header in such a way that the end-result is correct).
Just solder a few wires on the interconnection board, and then check! This is how I did it.
First I soldered all 16-pin and 40-pin headers on the board, then I only soldered the wires for "PAR HI" and "PAR LO"
from J1 to OUT1-2. I applied +5V to the PDP-11/70 front panel board (via the 8-pin Molex connector). As all LED driver
inputs are floating (not connected) all LEDs will be lit, except the LEDs that indicate the setting of the 2 rotary
switches. Then I plugged connector J1 from the PDP-11/70 board in the header on the connection board. When pin #9 of
the OUT1-2 header is connected to GND, the LED "PAR HI" should go off. Likewise, when pin #16 of the OUT1-2 header is
connected to GND, the LED "PAR LO" should go off.
When you checked this, you know you got the location of pin "A" and pin "B" on connector J1 correct. Now it is easy to
solder the wires for all DATA LEDs from J1 to OUT7-8. The way you do that is a matter of choice, but I soldered one entire
row (D0, D2, D4, D6 …) before I soldered the other row (D1, D3, D5 ...). This way you can better keep track of what you are
doing; I make less errors with this way of soldering lots of pins ...
The same goes for the pins of connector J2. Only connect "ADRS ERR" and "PAR ERR". Check that the correct LED goes off
when you ground the correct pin on the 16-pin header, then solder the other ADDRESS and some of the status LEDs.
More to follow ...