Hi guys,
According to the user guide the ports are 5V tolerant.
On my hobby project I want to connect a 5V analog modem
to LPC2148.
Should I connect them or should I place a level shifter
(which come in SMD cases and I can't do it directly).
And another question:
On OLIMEX P2148 board the two ports for hardware flow control (RTS/CTS)
are connected to 2 leds. Is there any clever way to
disconnect them form the leds so I can use them?
LPC2148 5V tolerant ports - analog modem
Started by ●December 2, 2011
Reply by ●December 2, 20112011-12-02
On 02.12.2011 08:12, koutote wrote:
> According to the user guide the ports are 5V tolerant. On my hobby project I
> want to connect a 5V analog modem to LPC2148. Should I connect them or
> should I place a level shifter
The only way to find out is to compare the LPC2148 data sheet to the
specification of the modem and see if the voltage levels are compatible.
--
Timo
> According to the user guide the ports are 5V tolerant. On my hobby project I
> want to connect a 5V analog modem to LPC2148. Should I connect them or
> should I place a level shifter
The only way to find out is to compare the LPC2148 data sheet to the
specification of the modem and see if the voltage levels are compatible.
--
Timo
Reply by ●December 2, 20112011-12-02
The voltages are not compatible...Modem outputs TTL 5V while LPC outputs I think
3.3V. However user guide states that LPC is tolerant to 5V.
The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
________________________________
"t...@gmail.com"
: l...
.: koutote
: 9:50 2 2011
: Re: [lpc2000] LPC2148 5V tolerant ports - analog modem
On 02.12.2011 08:12, koutote wrote:
> According to the user guide the ports are 5V tolerant. On my hobby project I
> want to connect a 5V analog modem to LPC2148. Should I connect them or
> should I place a level shifter
The only way to find out is to compare the LPC2148 data sheet to the
specification of the modem and see if the voltage levels are compatible.
--
Timo
The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
________________________________
"t...@gmail.com"
: l...
.: koutote
: 9:50 2 2011
: Re: [lpc2000] LPC2148 5V tolerant ports - analog modem
On 02.12.2011 08:12, koutote wrote:
> According to the user guide the ports are 5V tolerant. On my hobby project I
> want to connect a 5V analog modem to LPC2148. Should I connect them or
> should I place a level shifter
The only way to find out is to compare the LPC2148 data sheet to the
specification of the modem and see if the voltage levels are compatible.
--
Timo
Reply by ●December 2, 20112011-12-02
Hello Kostas,
--- In l..., Kostas Koutsouvelis wrote:
> The voltages are not compatible...Modem outputs TTL 5V while LPC
> outputs I think 3.3V. However user guide states
> that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn
> or cause operation failure of the LPC or not?
why do you think, the 5V modem output will burn
or cause operation failure of the LPC ?
When the modem outputs 5V and LPC can handle 5V (on this pin),
what is the problem ?
Best regards,
Martin
--- In l..., Kostas Koutsouvelis wrote:
> The voltages are not compatible...Modem outputs TTL 5V while LPC
> outputs I think 3.3V. However user guide states
> that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn
> or cause operation failure of the LPC or not?
why do you think, the 5V modem output will burn
or cause operation failure of the LPC ?
When the modem outputs 5V and LPC can handle 5V (on this pin),
what is the problem ?
Best regards,
Martin
Reply by ●December 2, 20112011-12-02
On 02.12.2011 13:11, Kostas Koutsouvelis wrote:
> The voltages are not compatible... Modem outputs TTL 5V while LPC outputs I think 3.3V.
You are confusing things badly. You would not connect modem outputs to LPC
outputs, would you. So that is not a relevant finding at all. What you should
be interested in is whether the input will be happy with the voltage the output
is driving it. The probable problem is that 3.3V driven by LPC output is not
enough for modem input. But nobody knows without comparing the specs.
> However user guide states that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
5V tolerant input tolerates 5V...
--
Timo
> The voltages are not compatible... Modem outputs TTL 5V while LPC outputs I think 3.3V.
You are confusing things badly. You would not connect modem outputs to LPC
outputs, would you. So that is not a relevant finding at all. What you should
be interested in is whether the input will be happy with the voltage the output
is driving it. The probable problem is that 3.3V driven by LPC output is not
enough for modem input. But nobody knows without comparing the specs.
> However user guide states that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
5V tolerant input tolerates 5V...
--
Timo
Reply by ●December 2, 20112011-12-02
I would be surprised if it didn’t work, most devices that claim TTL level
IO means TTL compatible input thresholds even if the device is CMOS, so VIh
should be around 2.4V, since the VOh for the LPC would be around 3.3V it should
be sufficient.
The other alternative also, if the 3V3 level is insufficient is to ignore level shifters, simply set the outputs mode to open drain mode and just use a pullup to 5V.
Regards
Phil.
From: l... [mailto:l...] On Behalf Of t...@gmail.com
Sent: 02 December 2011 12:05
To: l...
Cc: Kostas Koutsouvelis
Subject: Re: [lpc2000] LPC2148 5V tolerant ports - analog modem
On 02.12.2011 13:11, Kostas Koutsouvelis wrote:
> The voltages are not compatible... Modem outputs TTL 5V while LPC outputs I think 3.3V.
You are confusing things badly. You would not connect modem outputs to LPC
outputs, would you. So that is not a relevant finding at all. What you should
be interested in is whether the input will be happy with the voltage the output
is driving it. The probable problem is that 3.3V driven by LPC output is not
enough for modem input. But nobody knows without comparing the specs.
> However user guide states that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
5V tolerant input tolerates 5V...
--
Timo
The other alternative also, if the 3V3 level is insufficient is to ignore level shifters, simply set the outputs mode to open drain mode and just use a pullup to 5V.
Regards
Phil.
From: l... [mailto:l...] On Behalf Of t...@gmail.com
Sent: 02 December 2011 12:05
To: l...
Cc: Kostas Koutsouvelis
Subject: Re: [lpc2000] LPC2148 5V tolerant ports - analog modem
On 02.12.2011 13:11, Kostas Koutsouvelis wrote:
> The voltages are not compatible... Modem outputs TTL 5V while LPC outputs I think 3.3V.
You are confusing things badly. You would not connect modem outputs to LPC
outputs, would you. So that is not a relevant finding at all. What you should
be interested in is whether the input will be happy with the voltage the output
is driving it. The probable problem is that 3.3V driven by LPC output is not
enough for modem input. But nobody knows without comparing the specs.
> However user guide states that LPC is tolerant to 5V.
> The question is whether the 5V modem output will burn or cause operation failure of the LPC or not?
5V tolerant input tolerates 5V...
--
Timo
Reply by ●December 2, 20112011-12-02
----Original Message----
From: l...
[mailto:l...] On Behalf Of Phil Young
Sent: 02 December 2011 12:34 To: l...
Subject: RE: [lpc2000] LPC2148 5V tolerant ports - analog
modem
> I would be surprised if it didn't work, most devices that
> claim TTL level IO means TTL compatible input thresholds
> even if the device is CMOS, so VIh should be around 2.4V,
> since the VOh for the LPC would be around 3.3V it should
> be sufficient.
I've come across quite a few supposedly TTL compatible devices which do not sense 3.3V as a high level.
> The other alternative also, if the 3V3 level is
> insufficient is to ignore level shifters, simply set the
> outputs mode to open drain mode and just use a pullup to
> 5V.
I don't think that would work, there are protection diodes to Vcc on the pins which will still limit the output voltage to 3V3. I believe these remain active in open drain mode.
--
Tim Mitchell
From: l...
[mailto:l...] On Behalf Of Phil Young
Sent: 02 December 2011 12:34 To: l...
Subject: RE: [lpc2000] LPC2148 5V tolerant ports - analog
modem
> I would be surprised if it didn't work, most devices that
> claim TTL level IO means TTL compatible input thresholds
> even if the device is CMOS, so VIh should be around 2.4V,
> since the VOh for the LPC would be around 3.3V it should
> be sufficient.
I've come across quite a few supposedly TTL compatible devices which do not sense 3.3V as a high level.
> The other alternative also, if the 3V3 level is
> insufficient is to ignore level shifters, simply set the
> outputs mode to open drain mode and just use a pullup to
> 5V.
I don't think that would work, there are protection diodes to Vcc on the pins which will still limit the output voltage to 3V3. I believe these remain active in open drain mode.
--
Tim Mitchell
Reply by ●December 2, 20112011-12-02
I have to admit that I was mixing output with input ports...
According to TTL (wiki) everything higher than 2.2V should be regarded as high level (5V).
However I wouldn't be surprised if this is not the case.
I will try and I will let you know, although it will take some time.
Thanks
According to TTL (wiki) everything higher than 2.2V should be regarded as high level (5V).
However I wouldn't be surprised if this is not the case.
I will try and I will let you know, although it will take some time.
Thanks
Reply by ●December 2, 20112011-12-02
On 02.12.2011 14:44, Tim Mitchell wrote:
> I don't think that would work, there are protection diodes to Vcc on the pins
> which will still limit the output voltage to 3V3. I believe these remain active
> in open drain mode.
That would then make them NON-5V-tolerant, wouldn't it.
--
Timo
> I don't think that would work, there are protection diodes to Vcc on the pins
> which will still limit the output voltage to 3V3. I believe these remain active
> in open drain mode.
That would then make them NON-5V-tolerant, wouldn't it.
--
Timo
Reply by ●December 2, 20112011-12-02
