| ??? 01/25/05 06:04 Read: times |
#85722 - RS232 Signals Responding to: ???'s previous message |
Hi Nguyen,
The RS232 signals are not logic level signals as you think of them. The signals are nominally positive and negative 12 Volts corresponding to logic lo and hi (+12V of RS232 corresponds to 0V on the µ-controller side of the chip, and -12V of RS232 corresponds to 5V on the µ-controller side). Actually, I could be wrong about the RS232 voltages. Maybe it's ±15V and 0V to 3V. Someone who's more up on the subject will have to confirm the actual levels (TI specs their MAX232 inputs at ±30V), but the point is that it's not supposed to be 5V (or 3V, whichever) and 0V. The higher voltages were intended to maintain a higher signal to noise ratio over wires that were strung out across rooms. Hence the ± swing (greater difference between hi and lo). This is the reason you need the level shifter (the MAX232) in the first place. Good luck. Joe |
| Topic | Author | Date |
| Connect PC to AT89C52 | 01/01/70 00:00 | |
| RS232 Signals | 01/01/70 00:00 | |
| to Joe | 01/01/70 00:00 | |
| Null Modem | 01/01/70 00:00 | |
| To Joe again | 01/01/70 00:00 | |
| how have you wired the MAX232 up? | 01/01/70 00:00 | |
| Fundamentals of RS-232 Serial Comms | 01/01/70 00:00 | |
| App note | 01/01/70 00:00 | |
| Try this | 01/01/70 00:00 | |
link | 01/01/70 00:00 |