apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
busy is good !
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On Mon, Nov 11, 2013 at 3:10 AM, Christopher Havel laserhawk64@gmail.comwrote:
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel laserhawk64@gmail.com wrote:
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
yes. i thought of something. http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/7597
could you investigate, find some "educational" style electronics explanations online, as to why henrik's recommendation to use a pull-up resistor to 3.3V and a reversed-diode between the Tx UART and incoming Rx actually works? i'm attaching a small diagram showing the circuit.
it can then be added here: http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68#Requirements_fo...
also i think.... to avoid too big a voltage-drop it should be a zener diode otherwise it might interfere with the thresholds.
basically i think the way it works is that 0 logic level on UART is "positive voltage", and the Tx line "sucks" current down to GND in order to indicate a "1". therefore, normally (i.e. without the diode) current would be flowing *from* Rx *to* Tx if Tx is held at GND to indicate a "1"... so putting the diode in the circuit is... well... normal!
l.
On Tue, 2013-11-12 at 12:09 +0000, luke.leighton wrote:
On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel laserhawk64@gmail.com wrote:
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
yes. i thought of something. http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/7597
could you investigate, find some "educational" style electronics explanations online, as to why henrik's recommendation to use a pull-up resistor to 3.3V and a reversed-diode between the Tx UART and incoming Rx actually works? i'm attaching a small diagram showing the circuit.
it can then be added here: http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68#Requirements_fo...
also i think.... to avoid too big a voltage-drop it should be a zener diode otherwise it might interfere with the thresholds.
Henrik's idea should work - the diode should be a schottky diode with 0.2V to 0.3V drop as hinted in the drawing otherwise a 0.7V drop with a normal diode may be too high to allow a logic 0 to be registered.
The down side of the circuit is that the pull up resistor needs to be connected to the 3.3V line, which is inside the EOMA and not accessible.
Also - if higher baud rates don't work try decreasing the value of the resistor.
On Tue, Nov 12, 2013 at 1:58 PM, joem joem@martindale-electric.co.uk wrote:
On Tue, 2013-11-12 at 12:09 +0000, luke.leighton wrote:
On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel laserhawk64@gmail.com wrote:
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
yes. i thought of something. http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/7597
could you investigate, find some "educational" style electronics explanations online, as to why henrik's recommendation to use a pull-up resistor to 3.3V and a reversed-diode between the Tx UART and incoming Rx actually works? i'm attaching a small diagram showing the circuit.
it can then be added here: http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68#Requirements_fo...
also i think.... to avoid too big a voltage-drop it should be a zener diode otherwise it might interfere with the thresholds.
Henrik's idea should work - the diode should be a schottky diode with 0.2V to 0.3V drop as hinted in the drawing otherwise a 0.7V drop with a normal diode may be too high to allow a logic 0 to be registered.
The down side of the circuit is that the pull up resistor needs to be connected to the 3.3V line, which is inside the EOMA and not accessible.
... but if the circuit you did can do it with external resistors then that can also be arranged. as long as the pull-up voltage is greater than a 3.3v logic-level that should be enough. that leaves... 1.3v of wiggle-room... so splitting the resistors into say 1k and 10k in series and bringing out the pull-up in between the two of them should be sufficient, right?
Also - if higher baud rates don't work try decreasing the value of the resistor.
ok. thanks joe.
l.
On 11/12/2013 7:09 AM, luke.leighton wrote:
On Mon, Nov 11, 2013 at 2:10 AM, Christopher Havel laserhawk64@gmail.com wrote:
On 11/10/2013 9:08 PM, luke.leighton wrote:
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment. it's not personal: i just have far less time available and have to be very focussed. l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Sorry to hear you're so busy. Can I help? :D
yes. i thought of something. http://permalink.gmane.org/gmane.comp.hardware.netbook.arm/7597
could you investigate, find some "educational" style electronics explanations online, as to why henrik's recommendation to use a pull-up resistor to 3.3V and a reversed-diode between the Tx UART and incoming Rx actually works? i'm attaching a small diagram showing the circuit.
it can then be added here: http://elinux.org/Embedded_Open_Modular_Architecture/EOMA-68#Requirements_fo...
also i think.... to avoid too big a voltage-drop it should be a zener diode otherwise it might interfere with the thresholds.
basically i think the way it works is that 0 logic level on UART is "positive voltage", and the Tx line "sucks" current down to GND in order to indicate a "1". therefore, normally (i.e. without the diode) current would be flowing *from* Rx *to* Tx if Tx is held at GND to indicate a "1"... so putting the diode in the circuit is... well... normal!
l.
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
On Tue, Nov 12, 2013 at 4:53 PM, Christopher Havel laserhawk64@gmail.com wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
awesome. done. added to spec.
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
On 11/12/2013 2:51 PM, joem wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
arm-netbook mailing list arm-netbook@lists.phcomp.co.uk http://lists.phcomp.co.uk/mailman/listinfo/arm-netbook Send large attachments to arm-netbook@files.phcomp.co.uk
Pardon severe cranial densities here :P but what's wrong with sticking eg a 7803 in there somewhere to provide a little extra 3v3? Well, OK, a 7803 is probably a little more capable than absolutely necessary -- and it's not exactly efficient, either, to say the least -- but something *like* that (low current 3 pin 3v3 regulator) would tidy that little problem up quite nicely, now, wouldn't it? ;)
On Tue, Nov 12, 2013 at 7:51 PM, joem joem@martindale-electric.co.uk wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
no it is not. TTL 3v logic is somewhere around 2v for low. a small reduction (such as using another shottky diode) would be enough.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
great. 1.8+3.3=5.1 so the pull-up would be to 3.23V - enough to be definitely below 3.3v.
l.
On Tue, Nov 12, 2013 at 7:51 PM, joem joem@martindale-electric.co.uk wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
| no it is not. TTL 3v logic is somewhere around 2v for low. a small |reduction (such as using another shottky diode) would be enough.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
| great. 1.8+3.3=5.1 so the pull-up would be to 3.23V - enough to be |definitely below 3.3v.
Hmmmppp... pull ups don't work like you would expect under certain circumstances. I'm removing the 3rd diagram from here: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
On Tue, Nov 12, 2013 at 10:45 PM, joem joem@martindale-electric.co.uk wrote:
| great. 1.8+3.3=5.1 so the pull-up would be to 3.23V - enough to be |definitely below 3.3v.
Hmmmppp... pull ups don't work like you would expect under certain circumstances. I'm removing the 3rd diagram from here: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
ok mate. let us know if you think of something else. btw have you seen this? http://www.hobbytronics.co.uk/mosfet-voltage-level-converter
On Tue, 2013-11-12 at 22:45 +0000, joem wrote:
On Tue, Nov 12, 2013 at 7:51 PM, joem joem@martindale-electric.co.uk wrote:
Try this :) it popped up on Google pretty quickly --> http://www.hobbytronics.co.uk/schottky-logic-level-conversion
: awesome. done. added to spec.
Same problem - access to the 3.3V power line inside the EOMA needed.
| no it is not. TTL 3v logic is somewhere around 2v for low. a small |reduction (such as using another shottky diode) would be enough.
Anyway - 3rd diagram added - modified version of Henrik's diagram for the EOMA: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
| great. 1.8+3.3=5.1 so the pull-up would be to 3.23V - enough to be |definitely below 3.3v.
Hmmmppp... pull ups don't work like you would expect under certain circumstances. I'm removing the 3rd diagram from here: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
I don't understand what the guy is trying to say - construct and test is one way to remove doubt.
Also I'm not sure if the second diagram i did here http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair will work under all circumstances. If the UART TX pin defaults to a high value, the pull up will still drive the EOMA. You would need to press <CR> a few times to send low pulses to get the EOMA to power down. Alternatively connect to the internal 3.3V of the CPU as in first diagram - but sadly no access to that wire that feeds the CPU with 3.3V through the 68 pins. (Connecting to external 3.3V is no good - it will reproduce the said problem again.)
On Wed, Nov 13, 2013 at 11:40 AM, joem joem@martindale-electric.co.uk wrote:
If the UART TX pin defaults to a high value, the pull up will still drive the EOMA.
i think.... i think the pull-up needs to go on the other side of the diode.
through the 68 pins. (Connecting to external 3.3V is no good -
*sing-song* nooOOo, that's not good enough to say that: a solution has to be found because that's what the situation is, end of story.
l.
If the UART TX pin defaults to a high value, the pull up will still drive the EOMA.
i think.... i think the pull-up needs to go on the other side of the diode.
through the 68 pins. (Connecting to external 3.3V is no good -
*sing-song* nooOOo, that's not good enough to say that: a solution has to be found because that's what the situation is, end of story.
The second diagram is best: http://www.gplsquared.com/eoma_boot/eoma_boot.html#uart_repair
1. It uses power from MEB 2. It disconnects power to EOMA if the UART is pulled out 3. It can prevent power from pull up resistor reaching EOMA if the UART TX line is driven low. 4. It prevent power from PC reaching the EOMA through the UART TX line. 5. The worst case situation is UART holds TX line high and power reaches the EOMA through the pull up resistor. The EOMA may not power cycle properly if that happens.
But it is unlikely to get damaged because the 1.8K / 3.3K resistors places a limit on how high the voltage on the pin can rise. It can rise to about 3.3V and no more. The maximum current drain by CPU is about 2mA which is not enough to do damage (as far as I know).
All other solutions seen so far (other than connecting to 3.3V internal CPU power inside EOMA) is flawed because enough power can reach the CPU through the pull up resistor to keep it from shutting down properly. Some combinations will not allow the CPU to reset until the MEB power is cycled even if the UART is not connected. That is a dopey solution.
2013/11/11 luke.leighton luke.leighton@gmail.com
apologies to everyone on the list - you may have noticed i'm using brief and curt language at the moment.
Haven't noticed. But then again I'm Dutch. We're used to short and direct. ;-)
Good luck.
it's not personal: i just have far less time available and have to be very focussed. l.
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