| ??? 03/17/12 13:02 Read: times |
#186749 - You cannot match the weak internal active pull-up! Responding to: ???'s previous message |
David said:
So you need to match the 'internal pull-up' of P2. But you can't match it because the weak internal active pull-up is no resistor but a turned-on PMOSFET which lets a weak current flow. This current isn't stable at all, but shows huge variation from chip to chip and an awfull temperature dependency. The weak internal active pull-up is a "dirty" digital thing that cannot be used for any precise analog circuitry. By the way, the internal active pull-up stuff is even more complicated due to the action of the very weak internal active pull-up... Kai Klaas |
| Topic | Author | Date |
| Making a pulse with 3 different voltage level! | 01/01/70 00:00 | |
| No best but consider a voltage divider | 01/01/70 00:00 | |
| derivative with a DAC? | 01/01/70 00:00 | |
| derivative with configurable ports | 01/01/70 00:00 | |
| Thanks Per And Erik | 01/01/70 00:00 | |
| which derivative | 01/01/70 00:00 | |
| with an OPamp | 01/01/70 00:00 | |
| Thanks Erik | 01/01/70 00:00 | |
| So, you need to make -15V, 0V and +15V? | 01/01/70 00:00 | |
| Hi Dear Kai | 01/01/70 00:00 | |
| 74hc series | 01/01/70 00:00 | |
FPGA | 01/01/70 00:00 | |
| I think you can do it wih one resistor. | 01/01/70 00:00 | |
| Most 8051 Systems????? | 01/01/70 00:00 | |
| Well add a pull-up resistor then | 01/01/70 00:00 | |
| Would prefer to not have to match internal resistors | 01/01/70 00:00 | |
| You cannot match the weak internal active pull-up! | 01/01/70 00:00 | |
| Being pedantic. | 01/01/70 00:00 | |
| Hi David | 01/01/70 00:00 | |
| maybe a couple of mosfets ... | 01/01/70 00:00 | |
| Thanks Richard | 01/01/70 00:00 |