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Building the POST Code Project
WARNING: This section documents hardware MODIFICATIONS!
Neither I, other contributors, or FreeBSD take any responsibility for ANY
DAMAGE resulting from the use or mis-use of any information found on these
pages! If you don't understand any of the following DON'T attempt to do it!
Modifying the POST Card
The modifications to the POST card consist of adding a 2nd male DB-15
connector to the back bracket. Unfortunately the card places the existing
DB-15 connector in the middle of the bracket, so room for the 2nd DB-15
is tight. You might consider using a round high-density connector if you
can find something appropriate.
- Remove the POST card back braket and layout a hole for a 2nd DB-15
- Place it under the existing connector, as close as possible to
avoid hitting the motherboard with its bottom edge.
- Cut the hole, I used a DB-9 punch (twice per hole, not exactly
- Attach a 20" piece of 15 conductor IDC ribbon cable to a DB-15 male IDC
connector. Attach it to the bracket.
- Reconnect the bracket to the POST card.
- Attach a pair of wires to the PC bus NMI pin & ground on the POST card:
- Split the bottom 2 wires (pins 1 & 9) from the others, back to within
1/2" from the DB-15 connector.
- Clip off the ends approx. 2" from the DB-15, strip 1/4" of insulation.
- Solder one wire to the POST card's A1 bus connector. This is the
connector on the component side, closest to the back bracket. Note
that this "finger" exists on the board, but has no trace connected
to it. When soldering the wire be VERY careful to NOT let solder
flow over the entire finger, and to NOT create a large 'blob' of solder
that will damage the PC connector when the card is inserted.
- Solder the second wire to ground anywhere on the board. A convenient
place is the de-coupling capacitor about an inch above the NMI
connection. For reference, ground is brought to the card thru the
POST card's B1 bus connector, which is oppossite the NMI connector,
ie. on the solder side, closest to the back bracket.
- Attach berg .1" connectors to the IDC wires. You are effectively
recreating the wire harness that attaches from the cabinet, use that
as reference if necessary.
- Attach berg 1x2 connectors to each of the other 2 pairs of switch
wires, ie RESET & Soft-Power (ATX only).
- Attach berg 1x2 connectors to each of the 3 pairs of LED wires.
- Attach a berg 1x4 connector to the speaker wire pair, pins 1 & 4.
- The DB-15 pin #s are as follows:
DB-15 pin: IDC connector:
9 ground (NMI return)
10 ground (RESET return)
11 ground (Soft-Power return)
5 speaker return
6 yellow LED return (cathode)
13 yellow LED +5 (anode)
7 red LED return (cathode)
14 red LED +5 (anode)
8 green LED return (cathode)
15 green LED +5 (anode)
Building the Remote Box
The remote box will contain 3 switches, 3 LEDS, 2 7-segment LEDs and a speaker.
Note that both aluminum panels have a protective white covering on one side.
Make your layout marks on this side, and remove the covering after all tooling
- Layout the front panel:
- Draw a horizontal centerline.
- Mark switch positions at 1/2", 1-1/4" and 2" from the left side.
- Mark a rectangular cutout for the bezel. Exaxct position is a matter of
choice, I tried to keep the right border equal to the top & bottom
- Cut & punch the front panel.
- Mount switches & bezel.
- Layout the rear panel:
- Draw a horizontal centerline.
- Mark holes for the 2 DB-15 male connectors. Exact position is not
critical, I placed the centermost mounting holes of each DB-15
exactly 1/2" from the center of the panel.
- Cut & punch the rear panel.
- Mount 2 DB-15 male connectors, the wirewrap model goes on the right side
as viewed from the back. Connect a 10" piece of 15 conductor ribbon
cable to the IDC connector before mounting it to the panel.
- Solder the speaker wires to the speaker, mount speaker to bottom of
cabinet with glue. Optionally place "sound" holes in cabinet at
speaker mount position.
- Solder the switch wires to the 3 switches, maintaining the pinout
described in an earlier section.
- Cut the perfboard to the same size as an end panel. Place the 2, 14 pin
LED sockets in this board, so that they will sit behind the bezel
when the perfboard is placed into the cabinet slots immediately
behind the front panel. Place them to the right side, allowing
the 3 colored LEDs to be placed in a vertical row to the left.
Place the 3 colored LEDs in such a row, secure with glue.
- Cut a notch in the perfboard for the wires that go to the switches
on the front panel. Place the perfboard in the cabinent slots
immediately behind the front panel.
- Solder the LED wires to the 3 colored LEDS, maintaining the pinout
described in an earlier section.
- Connect the DB-15 wirewrap connector to the 2, 14 pin sockets.
- L1 is the least significant digit, on the left from the back
- L2 is the most significant digit, on the right from the back
DB-15 pin: 14 pin socket:
12 L1-3, L1-14, L2-3, L2-14 (+5 power)
unused 14 pin socket pins:
Building the cable
The cable between the POST card and the remote box consists
of 2 DB-15 IDC female connectors on each end of either 1 30/34 conductor ribbon
cable, or 2 15 conductor cables. Be sure to maintains pin-1 to pin-1
associations at each point in the chain.
Test and Final Assembly
Use an ohm meter to check the integrity of all wiring, from the berg connectors
at one end to the LEDs/switches/sockets on the other. Once you are sure
everything is OK, move the 7-segment LEDs from the POST card to the remote
Place the POST card into the computer. Replace the cabinet connectors with
those from the modified POST card as appropriate. I set the switches
up (from left to right) as Soft-power (red) , RESET (yellow) & NMI (orange).
After final safety inspection power the computer up, either from the main
power switch (AT) or with the remote box soft-power switch (ATX). Be
prepared for an immediate powerdown at any sign of trouble.
Test the RESET switch several times (before the system can boot the OS).
If all goes well boot single user and test the NMI switch. If ddb is
installed it should drop you into the debugger. Note that the NMI code
is NOT set up to expect this sort of behaviour yet, it assummes that NMI
is a hardware failure, and that you wont be bouncing right back to the OS
again! It might work, but its never been tested in this manner yet...
Observe any activity LEDs you hooked up. If they are not lighting up when
expected its probably a simple matter of changing the polarity on the MB
connection (ie. flip the berg connector around 180').
Finally you can test the 7-segment LEDs with testpost.c, available elsewhere
on this page.
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