VOGONS

Help with 486 Green Function / Turbo

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First post, by AncapDude

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Hi Vogons,

i am currently building a 486 rig based on the QDI V4P895P3/SMT V5.0 VLB mainboard with the well-known AMD 5x86-133.

The systems runs fine with the newest BIOS however i have some questions regarding turbo/green switch.

1. When pressing TURBO, the system completely stops while pressed and always operates at high speed when released, so there is no speed toggling here at all. Any advice why is that so?

2. The mobo has three connectors featuring "green mode". As i got this high screen tower with green switch (toggle switch), i would consider that as an alternative for the non-working turbo. But i am not sure if i should connect the switch to JP21 as it describes Pin1 as Ground and Pin2 as LOW/HIGH which indicates to me i should not short them with a toggle. Or am i wrong and this is safe?

3. JP32 seems i can connect another device to be included in the green mode as well. My VLB VGA has such a connector and i would consider wiring it here. Am i correct and is this a reasonable choice or not?

4. JP40 allows me to switch Green Clock between 8 or 16Mhz. It is part of the CPU type selection jumper matrix and for the 5x86 it is listed to set to 8 Mhz. Which clock is meant here? Bus clock?

I really would like to have a slowdown option for the system no matter if that is turbo or green function. The case just has the green button and no turbo button so i may wire that one to either option.

Thanks for your help.

Reply 1 of 6, by AncapDude

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I just tried to set SMI timeout in the BIOS to 15s and ran a benchmark. After 15s, the systems stops like when the turbo button is pressed and continues when i press a key. So it seems this isn't a slowdown option as well or it faces the same "bug" as the turbo function.

The case also has a green LED but it seems i cannot connect it anywhere. I think the case might be too new for this mobo and has green functions introduced with pentium or later that worked different.

Reply 2 of 6, by wbahnassi

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Green is not turbo. Connect the turbo switch to the TURBO SW on the front panel connectors array of the motherboard. Likewise Turbo LED indicates the turbo status not Green LED.

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Reply 3 of 6, by AncapDude

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Please read point 1 again.

Reply 4 of 6, by AncapDude

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Just tried to short JP21 today with a toggle switch, no effect at all like the turbo. The switch itsself works when connecting to reset.

Reply 5 of 6, by AncapDude

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OK, sadly the RetroWeb manual was wrong and Turbo Switch and LED Pins are swapped. So i shorted the LED connector all the time while testing TURBO. But now even on the correct PINs the system freezes instead of slowing down. I also measured that all LED connectors going with insane 5V. That fried all my LEDs. But i can see on measuring the Turbo LED that voltage drops when the switch is shorted. So Turbo LED indication may work, but i still don't know why the system isn't slowed down but freezed in non-turbo mode.

Reply 6 of 6, by pixel_workbench

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Try setting the CPU cache to write through mode, and test the turbo button. AFAIK turbo doesn't work when the CPU cache is in write back mode.

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