| ??? 08/09/06 17:14 Read: times |
#121915 - High or Low in keypad scanner? |
I've been looking at the keypad scanning materials I've encountered over the years and, while examining one popular scanner IC, I noted that, rather than, as is commonly assumed, driving the "current column" low, it drives one column at a time high instead. Now, not all encoders do this, but this one, a stock-numbered type from back in the '70's, so I can't give any reference to it, seems to have a 100K-ohm pulldown on the "columns" and scans the rows looking for a high.
Is this an arbitrary choice, or does it reflect some advantage of which I'm not aware? There are on pullups that I can measure or otherwise observe on any of the matrix lines. What's the benefit of pulling down rather than pulling up the one currently driven row/column? Any insights? RE |
| Topic | Author | Date |
| High or Low in keypad scanner? | 01/01/70 00:00 | |
| PNP? | 01/01/70 00:00 | |
| maybe with TTL, but what about CMOS? | 01/01/70 00:00 | |
| I would not, the user does | 01/01/70 00:00 | |
| that depends on how you scan the inputs | 01/01/70 00:00 | |
| physical/technological reasons | 01/01/70 00:00 | |
| What sorts of reasons? | 01/01/70 00:00 | |
| early MOS technology | 01/01/70 00:00 | |
| Maybe they did it... | 01/01/70 00:00 | |
| Oxymoron! | 01/01/70 00:00 | |
| you spoilt my joke now | 01/01/70 00:00 | |
| Jokes | 01/01/70 00:00 | |
| We are living in a TTL world... | 01/01/70 00:00 | |
| I don't know why this interests me, but ... | 01/01/70 00:00 | |
| a proverbial answer | 01/01/70 00:00 | |
| So you figure it's just a matter of preference? | 01/01/70 00:00 | |
| You really should get out more! | 01/01/70 00:00 | |
Yes, it's a second childhood ... or maybe a third | 01/01/70 00:00 |