S-100 Backplane V4 - 9-slot


This is the 9-slot S-100 Backplane V4 designed by Josh Bensadon. It is the 4th revision of RBC community S-100 backplane and incorporates lessons learned from other boards.


  • 9 slot
  • Active Termination (copied from V3)
  • 1st slot is spaced 1” from other slots to accommodate IMSAI Style chassis. All other slots are spaced the usual 0.75”
  • Mounting holes for ALTAIR and IMSAI chassis. Hole size 0.138” (6-32 screws
  • Two power connectors with different pin outs.
    • P1 with 0.2” (5.08mm) spacing. Hole Size 0.060”
    • P2 with 0.156” spacing. Hole Size 0.065”
  • Expansion Connectors with multiple function
    • Expansion IN/OUT
    • Test point
    • Active Termination
  • Jumpers to ground some S-100 pins as needed by IEEE-696.
    • Pins 20, 53 & 70. (Pin 53 on ALTAIR and IMSAI computers is needed for Front Panel operations and should not be grounded when using these front panels).
  • Thick board, approximately 0.100”.
  • S-100 connectors require 0.25” row spacing. Hole sized 0.040”.
  • Fused power.

Hardware Documentation

Board: s100_backplane_v4-brd.pdf

Schematic: s100_backplane_v4_schematic.pdf

KiCAD & Manufacturing Files: s100_backplane_v4.zip note - V4 KiCAD updates were made in PCB editor only, KiCAD file schematic does not reflect PCB.

Build Information

Josh Bensadon put together an excellent User's Manual for this board which includes construction notes and a Bill of Materials. The following sections are reproduced from this document.


The exact bill of materials will vary based on your desired build. You may choose to install less than all nine of the S-100 connectors. Active Termination is also optional with slower speed systems (4MHz or less), but a must have for high speed. Which power connector you choose is also optional and based upon your ultimate chassis design. Perhaps you already have one size or another of the connector and want to use that. With all the variations, the parts given in the BOM are only a single possibility, your build will vary.


The voltage rating on capacitors can be higher than shown; this will not affect the performance in any way. If you are ordering all the capacitors, then it is likely to be cheaper to order all the same voltage (say 16V), further, it will eliminate errors when building. Sometimes a capacitor rated at a higher voltage is actually cheaper than a lower rated one of the same capacitance. This can happen when it is more popular to order that higher voltage, hence production increases and cost per unit decreases.


All resistors are 1/4Watt. Trimmer pot has 3 leads, 0.200” spacing between ends and a middle pin that is 0.100” row offset. Eg. Digikey part number: 987-1065-ND


These are fast acting Micro Fuses (eg. Digikey Part number: F5580TR-ND). They are optional, you may simply install a jumper wire here if you choose not to use them, or if your power supply already has fused outputs. The exact values of the fuses depend on your S-100 build. Their purpose is to protect the power supply and circuit traces. As a general rule, they should not be higher than the maximum rated current output of your power supply. Here are some reasonable values, but the current demands of the boards you install in your S-100 will ultimately be your best guide. You may also choose to substitute these fuses with PTC type fuses.

Fuse Voltage Supply Rating
F1, F4 +8V 3 to 10 Amps
F3, F5 +16V 1 Amp
F2, F6 -16V 1 Amp
Expansion Connectors

The Front expansion connectors can be populated with pin headers as test points or used to extend another backplane board. The back expansion connector can be used to extend or terminate the bus as shown below.

Extending the bus on high speed systems (over 4Mhz) might present a problem as the connectors between two backplanes may cause undesired reflections. It has not been tested but the option is there for your choice to try. No guarantees of performance are given. Perhaps one way to minimize the medium transition is to use PCB mounted ribbon cables (eg. Digikey Part number 1658525-2-ND) instead of pin headers with connectors & ribbon cables.

Bill of Materials

Base Build
Part Description
Slot1-9 S-100 Connector. 0.25” row spacing
P1 6 Position Connector. 0.200” (5.08mm) Right angled connector under the slot cards
P2 6 Position Connector. 0.156”
F1-F3 Micro fuses for P1 Connector. See text Eg. Digikey p/n: F5580TR-ND
F4-F6 Micro fuses for P2 Connector. See text Eg. Digikey p/n: F5580TR-ND
D1-D3 LED’s. Your favorite type.
R15 4.7K Resistor
R16, 17 20K Resistor
JP1-3 2 Pin 0.100” Pin Header
JP1-3 Mini-Jumpers
Active Termination
Part Description
C1,C3 39uF / 25V Tantalum Capacitor
C2 0.47uF / 6.3V Tantalum Capacitor
C4-C8 39uF / 6.3V Tantalum Capacitor (see text)
IC1 LM7805 Voltage Regulator. Positive 5 Volts. TO-220
IC2 LM4250 Op Amp Q1 2N3906 PNP Transistor TO-92
Q2 2N3904 NPN Transistor TO-92
Q3 TIP29 NPN Power Transistor TO-220
Q4 TIP30 PNP Power Transistor TO-220
R1 2K Trimmer POT. 0.100” spacing, 0.100” row offset Eg. Digikey p/n: 987-1065-ND
R2 150K Resistor
R3,R5 560 Ohm Resistor
R4, R8 1K Resistor
R6, R7 910 Ohm Resistor
R9, R10 1.8K Resistor
RN1-12 270 Ohm Resistor Network. 9 pin (8 Resistors Bussed)
Reset Switch
Part Description
SW1 Small tactile PCB Mounted Momentary Push Button Switch
R18 470 Ohm Resistor
P3 2 Pin 0.100” Pin Header
JP4 3 Pin 0.100” Pin Header
Expansion Connectors
Part Description
Front Connectors 34 pin (2×17) 0.100 Pin Headers (for Test Pins)
Front Connectors 34 pin (2×17) 0.100 PCB Mounted Ribbon Cable Eg. Digikey Part number 1658525-2-ND
Back Connectors 34 pin (2×17) 0.100 PCB Mounted Ribbon Cable Eg. Digikey Part number 1658525-2-ND

Builder's Notes/Comments

Please use this space to add any notes/comments on this board that don't fit into the above sections. (Periodically, these comments may be re-arranged to be better incorporated into a new revision of the wiki page.) Please sign your comments using the wiki “Insert Signature” feature! — Andrew Bingham 2016/02/27 13:01

No images found.

File List

FilenameFilesizeLast modified
s100_backplane_v4-brd.pdf1.2 MiB2017/01/09 23:46
s100_backplane_v4-brd.png221.1 KiB2017/01/10 01:22
s100_backplane_v4-exp.png66.2 KiB2017/01/10 01:17
s100_backplane_v4-manual.pdf759.5 KiB2017/01/09 23:53
s100_backplane_v4-sch.pdf53.8 KiB2017/01/09 23:53
s100_backplane_v4.zip659.8 KiB2017/01/09 23:17

V1/V2/V3 Historical Files & Information

See the Historical page for information on the prior S-100 Backplane versions including V1 (6-slot), V2, and V3 (8-slot).

boards/s100/backplanev4/start.txt · Last modified: 2017/03/23 18:45 by jordi.solis
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