| ??? 04/27/07 17:50 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#138137 - An idea... Responding to: ???'s previous message |
Hi Hendryawan,
I would give the following scheme a try:  How does it work? Assume a 74LS245, which is NOT in tristate condition is driving the input, then the logic state at P1.1 does not matter, P1.0 is always reading the correct logic state at input (of course, correct for the inverting). So, toggling P1.1 from low to high and high to low does not change the state of P1.0! But, when the 74LS245 is in tristate condition, then it cannot drive the input pin at all. Then, the inverter at P1.1 can force the input pin to any desired level. So, when P1.1 is toggling from low to high, then P1.0 will do the same. When P1.1 is toggling from high to low, then P1.1 is doing the same. Means, you have to toggle P1.1 all the time, as fast as possible (but not faster than every 1µec, to allow stray capacitance to be charged), and look what happens at P1.0: If it changes its state in the same manner as P1.1, then the 74LS245 is in tristate condition. But, if the reading is stable, then the 74LS245 is not in tristate condition, but emits either low or high state. Of course, this scheme can only work, when the logic state at input is considerable slowlier changing its state than P1.1 can toggle! Also, a change can only be detected after up to two togglings of P1.1. As I do not know anything about your actual application, I cannot tell you whether this scheme will work for you or not. It's just an idea. Kai |
| Topic | Author | Date |
| tri state input reading | 01/01/70 00:00 | |
| tri-state | 01/01/70 00:00 | |
| Reading TriState | 01/01/70 00:00 | |
| Hi-Z reading | 01/01/70 00:00 | |
| Logic Probe Concept | 01/01/70 00:00 | |
| Window Comparator | 01/01/70 00:00 | |
| Build Or Buy | 01/01/70 00:00 | |
| Using Analogue Methods to test for Hi-Z | 01/01/70 00:00 | |
| Spare ADC and DAC on your micro? | 01/01/70 00:00 | |
| search found | 01/01/70 00:00 | |
| Some mistake | 01/01/70 00:00 | |
| 100k resistor | 01/01/70 00:00 | |
| An idea... | 01/01/70 00:00 | |
| Fundamental Logic and Hi-Z impedance | 01/01/70 00:00 | |
| Some thoughts on the tristate detection | 01/01/70 00:00 | |
| not 'the first', but THE problem | 01/01/70 00:00 | |
| Heisenberg | 01/01/70 00:00 | |
agreed | 01/01/70 00:00 | |
| thank you | 01/01/70 00:00 |