| ??? 05/08/07 18:00 Read: times |
#138849 - Here we go again ... Responding to: ???'s previous message |
Erik, you're providing a perfectly valid answer to a question that wasn't asked. Let's focus on what the O/P did ask.
This O/P wants to use the 74C922. I don't know why. It costs more than a typical small MCU. He probably already has one and that's why he wants to use it. It's VERY straightforward to read it in firmware. It's even possible to write the LCD directly from it without involving the MCU at all, if all he wants is a numeric output. Given that he wants to use the MCU to write the LCD, he simply has to (1) memory-map it, which I don't recommend, but in which case the nRD signal from the MCU should drive the negative-going OUTPUT-ENABLE pin or (2) he should use a port bit to drive the negative-going OUTPUT-ENABLE pin low immediately before reading the data bits and raise it immediately after he's read the data. What matters is his hardware implementation, and he has shed no light at all on how he's done that. As for the interrupt, well, until he figures out exactly what sort of an interrupt he's going to use, I recommend he focuses on learning how all this stuff works together. For that reason, I'd recommend he write the code in ASM before attempting it in 'C' just to ensure he knows what's going on. Clearly he doesn't know that now. RE |
| Topic | Author | Date |
| external interrupt using by keypad encoder 74c922 | 01/01/70 00:00 | |
| that code does not compile | 01/01/70 00:00 | |
| it is wotking now... | 01/01/70 00:00 | |
| reply | 01/01/70 00:00 | |
| strongly and totally disagree | 01/01/70 00:00 | |
| Have you carefully read the datasheet? | 01/01/70 00:00 | |
| what good would that do? | 01/01/70 00:00 | |
| Apparently, you haven't done that either, Erik | 01/01/70 00:00 | |
| Misread? | 01/01/70 00:00 | |
| 922 and 922 | 01/01/70 00:00 | |
| Here we go again ... | 01/01/70 00:00 | |
| Why ASM | 01/01/70 00:00 | |
| Fundamental misconception | 01/01/70 00:00 | |
| nope, here is the correction | 01/01/70 00:00 | |
| what about, for a change, answering a question? | 01/01/70 00:00 | |
| If you can\'t do it in ASM, you can\'t do it at all. | 01/01/70 00:00 | |
| LCD Routine take time. | 01/01/70 00:00 | |
| it is a good idea, but the problem in another... | 01/01/70 00:00 | |
what an understatement | 01/01/70 00:00 |