Learn from my mistake
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1. e oriented fel low I assumed that the problem was with pesky software or setup proto cols after all hardware is much more clear cut and what could have failed just by changing mo dems I spent a few hours studying and relearning the Hayes com mands and trying innumerable per mutations of command strings I noted that the manual says to be sure to set up the modem for re quest to send clear to send RTS www ednmag com CTS hardware handshaking and I set my drivers accordingly Nothing worked I was ready to send the mo dem back insisting that it was not working But my intuition said that the fact that the modem dialed and successfully connected indicated that it was not defective I put the project aside then start ed all over again In addition to the modem software and power adap ter the package came with an RS 232 cable which I had assumed I didn t need to use because I already had one that worked Then I no spoken assumptions you have made that may be incorrect Examine your biases I assumed that because the cable I had was not defective and because it supported my mo dem all the hardware in place was fine and therefore the problem was in the initialization parameters I could not have been more off base Finally look back at what you have learned In this case I got reac quainted with the AT command set as it applies to 56k modems We all make these kinds of obvi ous in retrospect mis2. ednmag comment By Bill Schweber Technical Editor Learn from my mistake recently spent the better part of a day upgrading the external modem on my Mac from a faithful but now slow V 32bis 14 4 kbps unit to a V 90 56 kbps unit Please don t tell me about how far behind the technolo gy curve my system was Why did this simple swap take so long Simple an oversight and shortsightedness on my part Briefly here s what happened I unplugged the slow modem re placed it with the new one and made no changes to anything else My strategy was that I should at least be able to verify the basic op eration of the new modem at the slower speed simply by swapping the old with the new just as you would change a light bulb Yet when I tried to get the modem op erating it only sort of functioned I could dial a bulletin board system or my Internet service provider and connect successfully but I couldn t get data to flow either from the high level of a Web browser or from a basic low level terminal emula tion package By looking at the in dicator lights on the modem front panel I did have a feeling that the modem was at least receiving data from the outside I took out the user manual and carefully studied the setup and troubleshooting sections Most of the sections deal with possible con figuration and initialization prob lems which you control with the Hayes compatible AT command set Being a hardwar
3. ng morning tak ing data and making scope meas urements at many points in the cir cuitry No consistencies or patterns existed and my notes gave me no clue as to what was not working or why After a lunch break I restart ed my investigative efforts from point zero and immediately found that the power supply which I neg lected to check was dead I never made that mistake again ever Contact me at bill schweber cahners com SEPTEMBER 30 1999 EDN 39
4. takes and it s good to have them periodically hit you over the head Such mistakes remind us that just because we think we know what s going on doesn t mean that what s going on EXPERIENCE TELLS YOU THAT YOU CAN FOCUS SO RAPIDLY ON ONE PRESUMED CAUSE THAT YOU CLOSE YOUR MIND TO OTHER POSSIBILITIES ticed that the manual says that the supplied cable includes the RTS CTS hardware handshake lines Oops the LED in my head flashed on I quickly tried the new cable and everything worked fine even at the highest speeds You can learn several lessons from my tale of woe brought on by my own incorrect assumptions Don t assume that an upgrade re quires nothing new if you are going to run it in the mode of the older unit In this case the new modem needed hardware handshaking and the cable to support it but the old er one didn t Dont keep hitting your head against the wall for too long only to follow the wrong path at the fork in the road I should have stopped playing variations of the Hayes command set theme much sooner than I did Walk away re ex amine everything and see what un is what we think Being tripped up by a basic cable is a humbling expe rience and the experience tells you that you can focus so rapidly on one presumed cause that you close your mind to other possibilities Many years ago when I was trouble shooting a nonfunctioning proto type of a P based system I spent an entire frustrati
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