| ??? 03/17/05 20:04 Read: times |
#89880 - Problems with PCF8574 input |
Hi,
I want to use a PCF8574 IO expander to do keyboard scanning. Before going for the total solution, I first wanted to test this method on a single IO expander input. I've used pin 0 (further referred to as P0), hence I'm sending 0x01 to the device to define P0 as an input. The testcircuit (simplified version of what I really want) is given below: 
When running my sw, I'm scanning every 50ms. the status of the port. When detecting a low or high, I visualise it by (de)activating a LED on another pin of the IO expander (not given in the circuit above). However, I'm experiencing strange problems. When starting the SW, I'm detecting a '1' on P0 and the LED is activated. So, that's OK, since I didn't press the switch. When pressing the switch, the level on P0 goes low (switch makes contact with ground) and the LED is deactivated. So, this is OK too. But when releasing the switch, the level on the pin P0 remains low!!! (measured this with a scope). And I don't understand this. It looks like the input is pulling the signal low once it has been connected to ground and isn't willing to release the line again! Because of this, I don't have any changes anymore on P0, whether I'm pressing the switch or not. I can only have it working fine, when I directly connect P0 to ground or +5Vdc, so no switch nor resistor involved! Can someone explain what's going wrong? I've tried already other values for the resistor, but nothing helps. Rgds, -- Geert |
| Topic | Author | Date |
| Problems with PCF8574 input | 01/01/70 00:00 | |
| best guess | 01/01/70 00:00 | |
| To Erik | 01/01/70 00:00 | |
| So.... | 01/01/70 00:00 | |
| To Jez Smith | 01/01/70 00:00 | |
| show the code | 01/01/70 00:00 | |
| To Oleg | 01/01/70 00:00 | |
| How to post code | 01/01/70 00:00 | |
| To Andy | 01/01/70 00:00 | |
| hmmmmmm | 01/01/70 00:00 | |
| To Jez | 01/01/70 00:00 | |
| RTFDS - using 8574 IO as inputs | 01/01/70 00:00 | |
| To J. Guy | 01/01/70 00:00 | |
| When is pin written ? | 01/01/70 00:00 | |
| My datasheet tells something different.. | 01/01/70 00:00 | |
| To Kai | 01/01/70 00:00 | |
| cutting through the fog | 01/01/70 00:00 | |
| To J. Guy | 01/01/70 00:00 | |
| Where is the difference between... | 01/01/70 00:00 | |
| To Kai | 01/01/70 00:00 | |
| Re:Problems with PCF8574 input | 01/01/70 00:00 | |
| Test it without having any communication | 01/01/70 00:00 | |
| To Kai | 01/01/70 00:00 | |
| Maybe good guess! | 01/01/70 00:00 | |
| To Medhi | 01/01/70 00:00 | |
| Switch terminology | 01/01/70 00:00 | |
| Thanks! | 01/01/70 00:00 | |
| Coonfoosed yeeet | 01/01/70 00:00 | |
| Contact arrangement - nothing else | 01/01/70 00:00 | |
| PCF8574 | 01/01/70 00:00 | |
| To Ben | 01/01/70 00:00 | |
| I have used the bugger often | 01/01/70 00:00 | |
| To Erik | 01/01/70 00:00 | |
| helloooooooooo !! | 01/01/70 00:00 | |
| To Erik | 01/01/70 00:00 | |
| Wager... | 01/01/70 00:00 | |
| To Grant | 01/01/70 00:00 | |
| The code... | 01/01/70 00:00 | |
| Thats told 'em :-) | 01/01/70 00:00 | |
| Frightend... ;-) | 01/01/70 00:00 | |
| Formatting | 01/01/70 00:00 | |
| Format flavours. | 01/01/70 00:00 | |
| Insanity | 01/01/70 00:00 | |
| Malaysian Grand Prix... | 01/01/70 00:00 | |
| Some update!!! | 01/01/70 00:00 | |
| Let me comment.... | 01/01/70 00:00 | |
| "fancy" code | 01/01/70 00:00 | |
| I'll Suggest... | 01/01/70 00:00 | |
| Pointers and structures | 01/01/70 00:00 | |
| C assumes int | 01/01/70 00:00 | |
| Followed the advice of Michael Karas... | 01/01/70 00:00 | |
| Why not assembly using? | 01/01/70 00:00 | |
| Assembler code | 01/01/70 00:00 | |
| Well... | 01/01/70 00:00 | |
| int | 01/01/70 00:00 | |
| Check Maxint ? | 01/01/70 00:00 | |
| Maxint | 01/01/70 00:00 | |
| Murdered quote | 01/01/70 00:00 | |
| I2C code | 01/01/70 00:00 | |
| Keil webpage | 01/01/70 00:00 | |
| i2c simulator | 01/01/70 00:00 | |
| Me to blame? | 01/01/70 00:00 | |
| not blaming you! | 01/01/70 00:00 | |
| Michael B. made a very usefull tool! | 01/01/70 00:00 | |
| hello | 01/01/70 00:00 | |
| Not aware? | 01/01/70 00:00 | |
| thank u | 01/01/70 00:00 | |
Name confusion... | 01/01/70 00:00 | |
| hi | 01/01/70 00:00 | |
| Damned, damned, damned... | 01/01/70 00:00 | |
| Ha, ha, ha, ha, ha .... | 01/01/70 00:00 | |
| Calico | 01/01/70 00:00 | |
| Pls. do so! | 01/01/70 00:00 | |
| Keyboard Calico | 01/01/70 00:00 | |
| Christmas | 01/01/70 00:00 | |
| Maybe it was .... | 01/01/70 00:00 | |
| Christmas Presents | 01/01/70 00:00 |