RS232 Loop Back
Loop back test for the RS232 section of the Inchworm.
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These instructions are for the people who are new to electronics.
Read, understand, and follow these instructions while I poke my finger in my eye.
Please understand what this test does prior to doing it. It is not a learn as you do sort of thing. I do not want you to ruin your inchworm. Proceed at your own risk.
1. Remove the 16F877(A).*
2. Hook the Inchworm to the PC with the serial cable.
3. Start hyperterm, select the correct com port.
4. Power up the Inchworm.
5. Note that when you type in hyperm window, nothing happens.
6. Jumper pin26 RX and pin25 TX on the PIC socket. ***
7. Type in the hyperterm window, you should see what you type.
If Hyperterm displays what you type with RX and TX jumpered and does not without the jumper.... then your RS232 cable is OK and the MAX232 is doing its job and providing TTL level ASCII to the PIC socket. This is good.
Problems
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If Hyperterm display the keys witout the jumper in place you have a short between RX and TX either before the MAX232 or between it and the PIC. Rare.
If Hyperterm does not display the keys with the jumper in place first check to see if maybe you have a good non-null-modem RS232 cable. Use an ohm meter to do this. Cable pins 2 and 3 should conduct and not be crossed.
If the cable is good you need to troubleshoot the RS232 section on the Inchworm. I will leave that to Bill.
* Check the PIC for bent pins. If either pin 25 or pin 26 is bent under you may have found your probloem.
*** Do NOT force a large wire into the PIC socket as if it were a breadboard. That would ruin the socket. Just hold the wire against the pins. If you can not type and hold the wire at the same time have some one else do the typing.
HTH
3v0