VOGONS


First post, by maxtherabbit

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This version of the board has unpopulated provisions for a PS/2 mouse - I would like to write up a guide for implementing PS/2 mouse on this board, but there are 4 pins on the mini-keyboard controller I have yet to identify. If you have one of these please check out my thread and help me see where the last 4 pins on this keyboard controller go!

It should only take 5 minutes with a multimeter - pins 1, 2, 18 and 23. Two of them should go to pins on the 5-pin header labeled CN3 next to the keyboard DIN. One of them should connect to IRQ12 on the ISA bus.

Via VT82C41N DIP-24 Keyboard Controller (KBC) - help completing pinout

Reply 1 of 30, by froller

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After applying multimeter to my LS-486e Rev:D I discovered that something is missing 😀

CN3 - 5-pin header
C5 and C7 - 47pF
L4 and L5 - 470uH
RP19 - 4 x 10kOhm
U29 - 74LS06
U30 - HT6542B or AMIKEY-2 (PS/2 keyboard and mouse controller)

And something is superfluous:

U28 - VT82C41N (keyboard-only controller)

I have not yet tried this 'cause I have a lot more other issues with this particular board. But I will as soon as I get through.
I'm going to update this post as I will get more information.

See comics below

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Overview
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Connector and LC-filter
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Keyboard controller and pull-up resistors
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Inverters
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Last edited by froller on 2021-02-12, 21:20. Edited 2 times in total.

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Reply 2 of 30, by maxtherabbit

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Wait! Before you remove that mini-KBC please check if pins 1, 2, 18, and 23 go anywhere! I have a hunch that 1 and 2 might just be mouse clock and mouse data

Reply 3 of 30, by froller

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maxtherabbit wrote on 2021-02-11, 02:31:

Wait! Before you remove that mini-KBC please check if pins 1, 2, 18, and 23 go anywhere! I have a hunch that 1 and 2 might just be mouse clock and mouse data

It doesn't seem they go anywhere at all. At least they certainly not connected to mouse data or mouse clock. They have approximately 1.5MOhm either to +5V or GND so they either not in use or even not connected inside a chip.

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Reply 5 of 30, by froller

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majestyk wrote on 2021-02-11, 09:50:

Be careful, the "clock" trace from pin2 ending with an "empty" noose does not mean it´s ending there, buth the trace is continuing in some in-between-layer underground.

Sure.
It goes to unsoldered inductor L5 located right under SIMM slots along with inductors for keyboard data and clock. And it also goes to unsoldered 4x resistor pack RP19 which contains pull-up resistor for both mouse clock and data and 2 other things.
And it's not pin 2. It's 39. 😀

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Reply 6 of 30, by froller

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Here's datasheet on Holtek HT6542B which looks a good replacement for VT82C41N.
LS-486e Rev:D has similar schematics the one shown on typical application page for PS/2 mobos except additional inductors between CN3 pins and KBC. For test purposes these inductors can be replaced with jumper wires.
Pull-up resistors and capacitors are as shown in datasheet.

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Reply 7 of 30, by maxtherabbit

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froller wrote on 2021-02-11, 09:43:
maxtherabbit wrote on 2021-02-11, 02:31:

Wait! Before you remove that mini-KBC please check if pins 1, 2, 18, and 23 go anywhere! I have a hunch that 1 and 2 might just be mouse clock and mouse data

It doesn't seem they go anywhere at all. At least they certainly not connected to mouse data or mouse clock. They have approximately 1.5MOhm either to +5V or GND so they either not in use or even not connected inside a chip.

So you are saying that pins 1, 2, 18 and 23 on the VT82C41N do not have continuity to any of the pins on the DIP40 footprint?

Reply 8 of 30, by froller

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maxtherabbit wrote on 2021-02-11, 13:49:

So you are saying that pins 1, 2, 18 and 23 on the VT82C41N do not have continuity to any of the pins on the DIP40 footprint?

I say VT82C41N pins 1, 2, 18 and 23 are not connected to DIP-40 pins 28 and 39.
DIP-40 pins 28 and 39 known to match HT6542B pins for mouse data and clock.
DIP-40 pins 28 and 39 connected to pull-up resistors RP19 and connector CN3 via inductors L5 and L6.
That perfectly matches typical application schematics of HT6542B.

The conclusion is: NO you can not tie PS/2 mouse to VT82C41N in the way you suppose to.

Unfortunately there is no datasheet on VT82C41N on the net.
The "similar" VT82C42 in fact is a DIP-40 monster like HT6542B and AMIKEY-2 but have some differences in its pinout.

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Reply 9 of 30, by maxtherabbit

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froller wrote on 2021-02-11, 16:12:

I say VT82C41N pins 1, 2, 18 and 23 are not connected to DIP-40 pins 28 and 39.

Ok but could you please check the other pins on the DIP40 footprint to see if they are connected to anything at all? My goal here is to document the VT82C41N

Reply 10 of 30, by froller

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maxtherabbit wrote on 2021-02-11, 16:18:

Ok but could you please check the other pins on the DIP40 footprint to see if they are connected to anything at all? My goal here is to document the VT82C41N

Had no luck. 🙁
Pins 1, 2, 18 and 23 of VT82C41N are neither connected to any pin of DIP-40 nor to ISA slot nor to any via in approximately 5cm around.
Anyway I'm gonna let you know if I found datasheet or some other info on VT82C41N.

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Reply 11 of 30, by maxtherabbit

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froller wrote on 2021-02-11, 21:04:
Had no luck. :( Pins 1, 2, 18 and 23 of VT82C41N are neither connected to any pin of DIP-40 nor to ISA slot nor to any via in ap […]
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maxtherabbit wrote on 2021-02-11, 16:18:

Ok but could you please check the other pins on the DIP40 footprint to see if they are connected to anything at all? My goal here is to document the VT82C41N

Had no luck. 🙁
Pins 1, 2, 18 and 23 of VT82C41N are neither connected to any pin of DIP-40 nor to ISA slot nor to any via in approximately 5cm around.
Anyway I'm gonna let you know if I found datasheet or some other info on VT82C41N.

Ok thank you for checking 😀

Reply 12 of 30, by maxtherabbit

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Oh by the way - as I'm sure you noticed from looking at the HT6542B datasheet's app notes - pins 28 and 39 are the mouse data and clock inputs. The chip also has output pins that need to be connected to the header (via the inductors of course) after being buffered through a 7406 inverter. There doesn't appear to be a footprint on the board for the inverter or any equivalent logic

Reply 13 of 30, by froller

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maxtherabbit wrote on 2021-02-12, 01:33:

Oh by the way - as I'm sure you noticed from looking at the HT6542B datasheet's app notes - pins 28 and 39 are the mouse data and clock inputs. The chip also has output pins that need to be connected to the header (via the inductors of course) after being buffered through a 7406 inverter. There doesn't appear to be a footprint on the board for the inverter or any equivalent logic

Luckily you noticed it!
Here's the footprint for 74LS06.

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Reply 15 of 30, by froller

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maxtherabbit wrote on 2021-02-12, 14:43:

Good catch. I don't own a rev D personally, my rev C has no such footprint. Trying to solder that SOP in between ISA slots is gonna suck

Many things become possible if you have soldering heat gun and roll of aluminum foil.
Just cover ISA slots with a paper napkin and 2 layers of foil and it should be more than enough to save them.

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Reply 16 of 30, by maxtherabbit

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froller wrote on 2021-02-12, 18:44:
maxtherabbit wrote on 2021-02-12, 14:43:

Good catch. I don't own a rev D personally, my rev C has no such footprint. Trying to solder that SOP in between ISA slots is gonna suck

Many things become possible if you have soldering heat gun and roll of aluminum foil.
Just cover ISA slots with a paper napkin and 2 layers of foil and it should be more than enough to save them.

yeah this should work, I prefer to drag solder SOP by hand when possible though

Reply 17 of 30, by froller

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maxtherabbit wrote on 2021-02-12, 14:43:

Good catch. I don't own a rev D personally, my rev C has no such footprint. Trying to solder that SOP in between ISA slots is gonna suck

Does your one have 4 72-pin SIMM slots and VT82C41N soldered between two lower ISA slots along with some 74-series logic chip?

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Reply 18 of 30, by maxtherabbit

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froller wrote on 2021-02-12, 20:58:
maxtherabbit wrote on 2021-02-12, 14:43:

Good catch. I don't own a rev D personally, my rev C has no such footprint. Trying to solder that SOP in between ISA slots is gonna suck

Does your one have 4 72-pin SIMM slots and VT82C41N soldered between two lower ISA slots along with some 74-series logic chip?

Indeed

Reply 19 of 30, by froller

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maxtherabbit wrote on 2021-02-13, 03:24:
froller wrote on 2021-02-12, 20:58:

Does your one have 4 72-pin SIMM slots and VT82C41N soldered between two lower ISA slots along with some 74-series logic chip?

Indeed

It looks fully packed and not suitable for modding. At least on photos.

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