CPCWiki forum
General Category => Amstrad CPC hardware => Topic started by: CraigsBar on 16:24, 17 January 21
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Quick Question time.
Is it possible to add a reset button to the GX4000? WIthout an expansion port of the Plus Machines to take the reset signal from are there any other places on the board that this can be found to take out to a momentary push switch to reset without pounding the power switch ;)
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I reckon 100% there is bit would need to look at the schematics.
What's the reason for wanting one?
I was playing navy seals today, man that is a hard ass game.
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Yeah, easy, just put a button between pin 26 of the CPU and GND.
Bryce.
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Yeah, easy, just put a button between pin 26 of the CPU and GND.
Bryce.
I was hoping it would be that easy... So glad you did not mention the ASIC!
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If it's "fat-fingered soldering" that you're worried about, remove the CPU before you solder. There's also a diode (D202) that goes to Pin 26 and you could solder the button to that point instead (the Cathode of the diode).
Bryce.
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I was hoping it would be that easy... So glad you did not mention the ASIC!
If you're doing it, you could document it and add it to the Wiki: https://www.cpcwiki.eu/index.php/Reset_Button
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If it's "fat-fingered soldering" that you're worried about, remove the CPU before you solder. There's also a diode (D202) that goes to Pin 26 and you could solder the button to that point instead (the Cathode of the diode).
Bryce.
Well it;s fitted and it works... I removed the Modulator at the same time because You know who used RF these day. This alsio left a nice hole in the case to mount the button without needing any new big hols drilline.
However it is not al 100% accurate as the reset on my plus machines. I guess because it is using the Reset signal not BusReset that I use on the CPC's expansion header. If Bus Reset available anywhere on the GX4000 board to increase the reliability of the button?
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That is the BUS reset of the GX4000. There is no other reset.
Bryce.
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That is the BUS reset of the GX4000. There is no other reset.
Bryce.
I don;t wish to question you Sir Bryce, But this Schematic tends to suggest to hat ASIC pin 159 is BRST as opposed to Z80 Reset. If i am reading this cirrectly BusReset can be picked up on one leg od R17 (Instead of sodlering to the Asic directly) or am I reading it wrong?
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OK. So I trusted continuity from asic 159 and resistor r17. Its a direct connection. Did the same on my plus (pin 159 and BRST on the expansion port) also a direct connection.
Tested with a patch cable. This reset r17 (asic side) to ground works perfectly.
Adjusted the soldering to move the cable to these points rather than the bottom of the board. 100% success. GX4000 reset button works perfectly on BRST from the asic.
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Ok, didn't realise there was a seperate BUSRESET for the ASIC.
Bryce.
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OK. So I trusted continuity from asic 159 and resistor r17. Its a direct connection. Did the same on my plus (pin 159 and BRST on the expansion port) also a direct connection.
Tested with a patch cable. This reset r17 (asic side) to ground works perfectly.
Adjusted the soldering to move the cable to these points rather than the bottom of the board. 100% success. GX4000 reset button works perfectly on BRST from the asic.
Hi, I'm also trying to add a reset button.
Wouldn't this create a short between +5v and the ground ? It seems the GX4000 lacks a 2.2K resistor between the BRST and +5v, like the 6128plus.
Would it also work with the C4CPC ? My guess is that the microcontroller on it won't be reset, and won't go back to the cartridge selection menu...
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Hi, I'm also trying to add a reset button.
Wouldn't this create a short between +5v and the ground ? It seems the GX4000 lacks a 2.2K resistor between the BRST and +5v, like the 6128plus.
Would it also work with the C4CPC ? My guess is that the microcontroller on it won't be reset, and won't go back to the cartridge selection menu...
The button goes between BSRT on the ASIC and Ground not +5v this is the exact same connection as is used on the BusReset on the expansion port of the 464+ and 6128+ and it behaves in the same way. so no it unfortunately does not reset the C4CPC, that still needs a power cycle.
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The button goes between BSRT on the ASIC and Ground not +5v this is the exact same connection as is used on the BusReset on the expansion port of the 464+ and 6128+ and it behaves in the same way. so no it unfortunately does not reset the C4CPC, that still needs a power cycle.
Edit: Oops, cannot paste images. I will try to attach them.
On the 6128 plus, the highlighted resistor prevents a short.
On the GX4000, there is no such resistor and the BRST is directly connected to 5V. Which means that bringing it to low would short.
Or am i missing something ?
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On the GX4000, there is no such resistor and the BRST is directly connected to 5V. Which means that bringing it to low would short.
Or am i missing something ?
You're not missing anything ;D
The proper way to do a reset on a GX4000 is to discharge the capacitor of the internal reset RC circuit that drives /SRST.
On my development GX, I do that by shorting the the common node of R17, R90 and D10 to GND.
It could also be done directly at C26 / Asic pin 156, but is a bit more stress for the capacitor as you are doing a real short.
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The button goes between BSRT on the ASIC and Ground not +5v this is the exact same connection as is used on the BusReset on the expansion port of the 464+ and 6128+ and it behaves in the same way. so no it unfortunately does not reset the C4CPC, that still needs a power cycle.
Early C4CPC (90% of the 1st batch) does not see the reset.
There is no direct way of getting the reset. On the later version, I've implemented a system in the PLD that detect it indirectly through the ACID signals.
But this does not reset the microcontroller either, just inform it that the CPC has reset.
By default, the CPC just ignore it so when you use the system cartridge it will reboot immediately. Only CprSelect takes advantage of it and is reloaded on a reset.
I can update your card if you want, but for that you have to ship it back to me ;D
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Early C4CPC (90% of the 1st batch) does not see the reset.
There is no direct way of getting the reset. On the later version, I've implemented a system in the PLD that detect it indirectly through the ACID signals.
But this does not reset the microcontroller either, just inform it that the CPC has reset.
By default, the CPC just ignore it so when you use the system cartridge it will reboot immediately. Only CprSelect takes advantage of it and is reloaded on a reset.
I can update your card if you want, but for that you have to ship it back to me ;D
oh hell yes please. Can you update Both of them! I have 2 you see.
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oh hell yes please. Can you update Both of them! I have 2 you see.
No problem. PM ;)
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On my development GX, I do that by shorting the the common node of R17, R90 and D10 to GND.
Nice ! That's where I will put my reset button then. Since my model is a French one, it has a nice empty hole at the back, ready to be used that way. :)
There is no direct way of getting the reset
It may have been possible to cut the track providing 5v to the cartridge and add a mosfet tied somewhere that get low on reset to power it. What an ugly hack... :o
I can update your card if you want, but for that you have to ship it back to me
Definitely ! I guess there is no easier way to reprogram the PLD ?
EDIT: It looks I'm lucky, my C4CPC resets correctly ! Yay!
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I wanted to add a picture of where i soldered the reset button, but it said there was already an attachement with the same name.
A renaming later, here is where the button was soldered.
Sometimes, the reset is not really complete and the C4CPC displays a bit of garbage in the path area, or sometimes it doesn't detects the reset, but overall, it works really well!
Thanks a lot, the capacitors on the power circuitry are also thanking you! :)
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Sometimes, the reset is not really complete and the C4CPC displays a bit of garbage in the path area, or sometimes it doesn't detects the reset, but overall, it works really well!
Yes, these are know issues, and why the feature is not official :laugh:
A long reset usually prevent this from happening.
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Should I add the picture describing where to solder the button to this page ?
https://www.cpcwiki.eu/index.php?title=Reset_Button