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Discussion Groups | LPC2000 | LPC2148 JTAG pin configuration
Discussion group dedicated to the Philips LPC2000 family of ARM MCUs
LPC2148 JTAG pin configuration - Sutton Mehaffey - Feb 20 14:26:10 2008
I have pullups on my JTAG lines (works fine), but noticed that in the
pin definitions on page 73 of the user manual that the JTAG pins
already have pullups on them. Is this when they are defined as GPIO
or do they have them when configured as JTAG? If I don't really need
them, I want to remove my 10K pullups from my board.
Sutton
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pin definitions on page 73 of the user manual that the JTAG pins
already have pullups on them. Is this when they are defined as GPIO
or do they have them when configured as JTAG? If I don't really need
them, I want to remove my 10K pullups from my board.
Sutton
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
Re: LPC2148 JTAG pin configuration - Tom Walsh - Feb 20 22:04:13 2008
Sutton Mehaffey wrote:
>
> I have pullups on my JTAG lines (works fine), but noticed that in the
> pin definitions on page 73 of the user manual that the JTAG pins
> already have pullups on them. Is this when they are defined as GPIO
> or do they have them when configured as JTAG? If I don't really need
> them, I want to remove my 10K pullups from my board.
>
Well... There is the empirical way to find out if it is true or not.
Since a logic 1 for the LPC2148 (ViH) is about 2 volts, and you assume
that a 10K pullup goes to a +3.3volt rail. Remove your 10K pullup from
one of the JTAG pins, then, assuming a voltage divider would be needed
to GND on that pin, put a 20K resistor from the pin to GND. Then
measure the voltage. You should see about 2.2volts there.
That should give you about 110ua of drain on that pin.
TomW
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )
>
> I have pullups on my JTAG lines (works fine), but noticed that in the
> pin definitions on page 73 of the user manual that the JTAG pins
> already have pullups on them. Is this when they are defined as GPIO
> or do they have them when configured as JTAG? If I don't really need
> them, I want to remove my 10K pullups from my board.
>
Well... There is the empirical way to find out if it is true or not.
Since a logic 1 for the LPC2148 (ViH) is about 2 volts, and you assume
that a 10K pullup goes to a +3.3volt rail. Remove your 10K pullup from
one of the JTAG pins, then, assuming a voltage divider would be needed
to GND on that pin, put a 20K resistor from the pin to GND. Then
measure the voltage. You should see about 2.2volts there.
That should give you about 110ua of drain on that pin.
TomW
(You need to be a member of lpc2000 -- send a blank email to lpc2000-subscribe@yahoogroups.com )