Since the failed experiments with the initial version of the 32-bit 80386DX ISA Single Board Microcomputer, I always wanted to build a ISA signal view interface card. And while
I don't have a logic analyzer moving the oscilloscope or the logic analyzer next to one of my DIY PCs is insanely difficult, I decided to use LEDs as a spartan form of optical signal analysis. Naturally this project is a LED eater. Thus I decided to give up on displaying the states of the ISA address and data bus. I only implemented the rest of the ISA signals.
As a side note, I always wanted to be able to visually observe triggering of the IRQ and DRQ signals. Especially when a sound card is requesting its appropriate interrupt. Also I am very curious to see if the VGA vertical retrace interrupt (signal IRQ9) is ever active.
Here are the hardware specifications.
This project is very simple and the design of the schematic posed no real issues. However it took a lot of time to draw. I did the complete manual routing of the PCB tracks in four hours or so. Pretty much a straightforward job.
Let's move on with the project.
Disclaimer: I reserve the right to change the schematic diagram, the PCB layout, or the implementation without further notice. This is an entirely hobby do-it-yourself design and I am not responsible for any damage made by any possible mistake in any version or revision of the schematics or PCB layouts. Since it is an advanced microelectronics project, it requires very good assembly and debugging skills. In addition I cannot offer any further technical support other than the contents of this article.
This project is in its final stage.
Current iteration of ASSY. 2486-SVIF-901 is VER. 1.0 REV. B
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Laudatur ab his, culpatur ab illis. This project is provided as-is and is not for commercial purposes. It reflects my experimental work in microcomputer system design and should be treated as such. I release the schematic and circuit boards to the public for educational purposes. I did all this on my expense and in my free time. So if you like my work, please consider a donation.
Fig. 1: Electrical Principial Schematic
Fig. 2: Top Silkscreen
Fig. 3: Top Layer Printed Circuit Board
Fig. 4: Inner Bottom Layer Printed Circuit Board
Fig. 5: Inner Top Layer Printed Circuit Board
Fig. 6: Bottom Layer Printed Circuit Board
Fig. 7: Top Layer Printed Circuit Board - Simulation
Fig. 8: Bottom Layer Printed Circuit Board - Simulation
Here are the Gerber files compressed in a .ZIP archive.
Please note that the file naming convention that I used is what OSHPark normally expects.
You can also order the printed circuit board directly from OSHPark by following the link in the bill of materials below.
Compressed Gerber Files: isa-sv-interface.zip
The following list contains the parts that are required to assemble this ISA signal view interface card.
|ISA SIGNAL VIEW INTERFACE|
|Printed Circuit Board||ASSY. 2486-SVIF-901||1||VER. 1.0 REV. B||Order from OSHPark|
|IC1-IC8||74F240||8||Octal 3-state Inverter||595-SN74F240N|
|C1-C8||100 nF / 50 V||8||MLCC||80-C322C104M5R-TR|
|C9-C17||10 uF / 25 V||8||Tantalum Capacitor||80-T350E106M025AT|
|RN1, RN3, RN4||8 x 470 Ω||3||Bussed Resistor Network||652-4609X-1LF-470|
|RN2, RN5||6 x 470 Ω||2||Bussed Resistor Network||652-4607X-1LF-470|
|RN6||4 x 470 Ω||1||Bussed Resistor Network||652-4605X-1LF-470|
|RN6||7 x 470 Ω||1||Bussed Resistor Network||652-4608X-1LF-470|
|LED1-LED7||5 mm Red LED||7||DMA Acknowledge Signals||755-SLR-56VC3F|
|LED8-LED14||5 mm Green LED||7||DMA Request Signals||755-SLR-56MC3F|
|LED26-LED34, LED36, LED38, LED39||5 mm Red LED||12||Inverted Signals||755-SLR-56VC3F|
|LED15-LED25||5 mm Orange LED||11||IRQ Signals||755-SLR-56DC3F|
|LED35, LED37, LED40-LED42, LED45||5 mm Green LED||6||Non-inverted Signals||755-SLR-56MC3F|
|LED43, LED44||5 mm Yellow LED||2||Clock Signals||755-SLR-56YC3F|
Alternatively you can use the following link to the Mouser project that I created for this ISA card. It should make ordering of parts and removing typing faults pretty easy.
Mouser Project: ISA SIGNAL VIEW INTERFACE
Lately I have observed that Mouser discontinued some of the parts in the list above. If you decide to build this project, then you need to find alternatives. It is out of my scope to maintain the correctness of the parts list above.
Here is a list of things you need to pay attention to should you decide to build such ISA signal view interface.
The printed circuit board assembly holds just a bunch of buffers and a lot of LEDs. I used 74F series ICs as buffers because of their small propagation delay. I don't ever expect to detect with the bare eye any high-speed signal switching on and off a certain LED. But why not?
So, in short, the principle of operation is like this: as soon as a certain signal is present on the ISA bus, it passes through a buffer and its respective LED turns on. Some of the LEDs will flicker with such a high frequency that they will appear as always on (think CLK and OSC signals). Some other LEDs will be quasi-permanently off (think IRQ9 or RESET signals).
In addition, active low signals are re-inverted so that their respective LEDs will be lit only when the signal is actually active.
The PCBs have arrived from the Factory. Now on to the assembly procedure. As with all large PCBs, the pictures present a certain amount of barrel distortion. I took them with my Nokia 6.1 mobile phone.
This is the bare 4-layer PCB.
I started soldering the passive components.
IC sockets follow next.
And the final assembled product. This card will surely help me debug my x86 system designs. And when I am done with debugging, it will provide nice ambient ligthing inside the case of my 32-bit 80386DX ISA Single Board Microcomputer system.
This section lists the project version and revision history.
Copyright © 2004- Alexandru Groza
All rights reserved.
VER. 1.0 | REV. A