Forums

CPLD input

Started by Hans Maier April 25, 2004
Does a CPLD Input source current ? When I measure the voltage
at my CPLD input pin, it is somewhere in the 3V range. When I connect
it to ground, it sources about 50 mA. Is that normal ? I thought an
input should not behave like this ..!?

	
Hans,

I would call that an output, or a broken input.

Austin

Hans Maier wrote:
> Does a CPLD Input source current ? When I measure the voltage > at my CPLD input pin, it is somewhere in the 3V range. When I connect > it to ground, it sources about 50 mA. Is that normal ? I thought an > input should not behave like this ..!? > >
>I would call that an output, or a broken input.
Yes, this is driving me mad .... It is configured as input, and it WORKS as input. If I pull it down to ground, the logic detects the low level. Could it still be broken ? How could I break an input ? There are only 5V on the board ....And the rest of the chip works just fine ....
Hans Maier wrote:

>>I would call that an output, or a broken input. > > > Yes, this is driving me mad .... > > It is configured as input, and it WORKS as input. If I > pull it down to ground, the logic detects the low level. > > Could it still be broken ? How could I break an input ? > There are only 5V on the board ....And the rest of the > chip works just fine ....
You could clarify if your 50mA meant 50 microamps, or 50 milliamps. Many times I've seen the greek 'u' in uA morph into mA on the internet as it jumps fonts.... 50uA could be a normal pin pullup, 50mA sounds like the PFET is on. A simple test is to try moving the function to another pin, or simply swap the pin allocates (two same-class pins). If the problem stays with the pin, it's likely to be chip related, if it moves with the function, suspect something in your code... -jg
> You could clarify if your 50mA meant 50 microamps, or >50 milliamps. Many times I've seen the greek 'u' in uA >morph into mA on the internet as it jumps fonts.... > 50uA could be a normal pin pullup, 50mA sounds like >the PFET is on.
it is 0.050 A or 50 milliamps
> A simple test is to try moving the function to another pin, > or simply swap the pin allocates (two same-class pins).
Thanks I will do that.
> If the problem stays with the pin, it's likely to be >chip related, if it moves with the function, suspect something >in your code...
code is very simple: VCC_SENSE: in std_logic; -- sense power
Here's a weird thought...  Try VOLT_SENSE: in
              -- sense power


"Hans Maier" <Hans@Maier.com> wrote in message
news:1f8t80lcr6kj8ghv4dao4qb6spbfhvrct1@4ax.com...
> > You could clarify if your 50mA meant 50 microamps, or > >50 milliamps. Many times I've seen the greek 'u' in uA > >morph into mA on the internet as it jumps fonts.... > > 50uA could be a normal pin pullup, 50mA sounds like > >the PFET is on. > > it is 0.050 A or 50 milliamps > > > > A simple test is to try moving the function to another pin, > > or simply swap the pin allocates (two same-class pins). > > Thanks I will do that. > > > If the problem stays with the pin, it's likely to be > >chip related, if it moves with the function, suspect something > >in your code... > > code is very simple: > > VCC_SENSE: in std_logic; -- sense power > >
Thanks for your help, It actually WAS a broken input.
The behaviour is OK when I use a new chip ..


>Here's a weird thought... Try VOLT_SENSE: in > -- sense power > > >"Hans Maier" <Hans@Maier.com> wrote in message >news:1f8t80lcr6kj8ghv4dao4qb6spbfhvrct1@4ax.com... >> > You could clarify if your 50mA meant 50 microamps, or >> >50 milliamps. Many times I've seen the greek 'u' in uA >> >morph into mA on the internet as it jumps fonts.... >> > 50uA could be a normal pin pullup, 50mA sounds like >> >the PFET is on. >> >> it is 0.050 A or 50 milliamps >> >> >> > A simple test is to try moving the function to another pin, >> > or simply swap the pin allocates (two same-class pins). >> >> Thanks I will do that. >> >> > If the problem stays with the pin, it's likely to be >> >chip related, if it moves with the function, suspect something >> >in your code... >> >> code is very simple: >> >> VCC_SENSE: in std_logic; -- sense power >> >> >