lauren%rand-unix@vortex.UUCP (02/12/84)
So bunky, you say you got yourself a Racal-Vadic triple modem (3451-series) and you have some problems with it? You say that sometimes in auto-answer mode it seems to hang offhook, making it impossible for any new calls to arrive? You say that when this happens it refuses to respond to DTR and only resets if you cycle the power or fiddle with the mode toggle switch (if you have one, that is)? Is that what's bothering you, bunky? WELLLLL! Lift up your head and greet the sun, 'cause a solution does exist -- and it doesn't even involve hydrochloric acid or jackhammers! Seriously, though, many persons have reported problems with triple modems getting into a strange wedged condition from which it is difficult to escape. Both manual dial and autodial triples have shown this behavior, which is characterized by the modem being offhook, sending a 212 carrier, and having both the HS and DSR lights lit. Only cycling the power or performing a software reset (by flipping the toggle switch between auto and manual on the autodial modems) will clear this condition; the modem is oblivious to DTR. After having this occur repeatedly on the main Vortex dialup line, I started harassing the engineers up at Racal. Actually, they were quite helpful, once they realized that I knew what I was talking about and hadn't plugged the RJ-11C phone plug into an AC wall outlet! After talking with three different engineers and having them duplicate the problem on their test benches, we arrived at the cause of the problem and a (simple) solution. The problem is caused by a "hole" in the triple modem protocol select algorithm. Under certain random timing conditions, the modem may be "fooled" into entering a pseudo-originate mode during its answer-mode operations. The exact reasons are too complex to go into here, but the cure is straightforward: Inside the modem, option dip switch A1 is described by the manual as: "Attended/Unattended Disconnect -- Set to Attended [ON] for Auto Dial modems. (Unattended setting relates to manual originate operation only.)" DON'T YOU BELIEVE IT! This switch also affects the handling of DTR during answer mode processing. The "normal" setting of this option (as set by the "standard-options" switch A6) is ON (Attended). This is WRONG for almost all operations. For both auto-dial and non-autodial triple modems, this option should normally be set to OFF (Unattended). The only side effect of this is that if you attempt to use the modem in a MANUAL originate mode, you will probably have to supply DTR at the RS232 interface (big deal!) If you leave A1 OFF, the answer mode wedging problem should vanish! Auto-dial operations on auto-dial modems should work as always. NOTE: If your triple has switch A6 OFF, then "standard-options" mode is ENABLED and the remaining A and B switches are ignored. In order to change the state of A1 to OFF, you must also turn switch A6 ON to disable "standard-options" and make sure that all other switches are set appropriately. I recommend the following settings (some of these are NOT the default settings): A1 -- OFF (Unattended -- fixes the answer wedge problem) A2 -- OFF (Do NOT respond to remote test) [do you want everyone in the universe "testing" your modem for you?] A3 -- ON (10 bit chars -- this is normal) A4 -- ON 103 operation enabled A5 -- OFF (10 bit chars -- this is normal) A6 -- ON Disable standard-options (enables all other switches) A7 -- ON Auto-disconnect on loss of carrier enabled B1 -- OFF Local digital loopback select (ignored when not testing) B2 -- OFF DTR controlled from RS232 interface B3 -- OFF Originate and Answer modes allowed B4 -- OFF 1204 bps speed (this is normal) B5 -- ON Auto-disconnect/Abort timer enabled B6 -- OFF Asynchronous operation B7 -- ON DSR off in test (ignored when not testing) In addition, I recommend the following two jumper changes on the BOTTOM pc board: Insert jumper "r" -- enable data rate indicator on RS232 pin 12 Remove jumper "ag" -- do not tie carrier detect high (RS232 pin 8) ------ The "wedged" condition mentioned above, being related to a rather random timing window, is more likely to have been seen on modems that have a high volume of calls than on low volume incoming lines. However, it occurs frequently enough that I recommend the option change for all triple modems being used for incoming calls. Be sure to let me know if you have any questions about or problems with this info. I hope it's of some use, bunky... --Lauren--
lauren@vortex.UUCP (Lauren Weinstein) (02/21/84)
Reposting due to failure of SRI-UNIX gateway... --- So bunky, you say you got yourself a Racal-Vadic triple modem (3451-series) and you have some problems with it? You say that sometimes in auto-answer mode it seems to hang offhook, making it impossible for any new calls to arrive? You say that when this happens it refuses to respond to DTR and only resets if you cycle the power or fiddle with the mode toggle switch (if you have one, that is)? Is that what's bothering you, bunky? WELLLLL! Lift up your head and greet the sun, 'cause a solution does exist -- and it doesn't even involve hydrochloric acid or jackhammers! Seriously, though, many persons have reported problems with triple modems getting into a strange wedged condition from which it is difficult to escape. Both manual dial and autodial triples have shown this behavior, which is characterized by the modem being offhook, sending a 212 carrier, and having both the HS and DSR lights lit. Only cycling the power or performing a software reset (by flipping the toggle switch between auto and manual on the autodial modems) will clear this condition; the modem is oblivious to DTR. After having this occur repeatedly on the main Vortex dialup line, I started harassing the engineers up at Racal. Actually, they were quite helpful, once they realized that I knew what I was talking about and hadn't plugged the RJ-11C phone plug into an AC wall outlet! After talking with three different engineers and having them duplicate the problem on their test benches, we arrived at the cause of the problem and a (simple) solution. The problem is caused by a "hole" in the triple modem protocol select algorithm. Under certain random timing conditions, the modem may be "fooled" into entering a pseudo-originate mode during its answer-mode operations. The exact reasons are too complex to go into here, but the cure is straightforward: Inside the modem, option dip switch A1 is described by the manual as: "Attended/Unattended Disconnect -- Set to Attended [ON] for Auto Dial modems. (Unattended setting relates to manual originate operation only.)" DON'T YOU BELIEVE IT! This switch also affects the handling of DTR during answer mode processing. The "normal" setting of this option (as set by the "standard-options" switch A6) is ON (Attended). This is WRONG for almost all operations. For both auto-dial and non-autodial triple modems, this option should normally be set to OFF (Unattended). The only side effect of this is that if you attempt to use the modem in a MANUAL originate mode, you will probably have to supply DTR at the RS232 interface (big deal!) If you leave A1 OFF, the answer mode wedging problem should vanish! Auto-dial operations on auto-dial modems should work as always. NOTE: If your triple has switch A6 OFF, then "standard-options" mode is ENABLED and the remaining A and B switches are ignored. In order to change the state of A1 to OFF, you must also turn switch A6 ON to disable "standard-options" and make sure that all other switches are set appropriately. I recommend the following settings (some of these are NOT the default settings): A1 -- OFF (Unattended -- fixes the answer wedge problem) A2 -- OFF (Do NOT respond to remote test) [do you want everyone in the universe "testing" your modem for you?] A3 -- ON (10 bit chars -- this is normal) A4 -- ON 103 operation enabled A5 -- OFF (10 bit chars -- this is normal) A6 -- ON Disable standard-options (enables all other switches) A7 -- ON Auto-disconnect on loss of carrier enabled B1 -- OFF Local digital loopback select (ignored when not testing) B2 -- OFF DTR controlled from RS232 interface B3 -- OFF Originate and Answer modes allowed B4 -- OFF 1204 bps speed (this is normal) B5 -- ON Auto-disconnect/Abort timer enabled B6 -- OFF Asynchronous operation B7 -- ON DSR off in test (ignored when not testing) In addition, I recommend the following two jumper changes on the BOTTOM pc board: Insert jumper "r" -- enable data rate indicator on RS232 pin 12 Remove jumper "ag" -- do not tie carrier detect high (RS232 pin 8) ------ The "wedged" condition mentioned above, being related to a rather random timing window, is more likely to have been seen on modems that have a high volume of calls than on low volume incoming lines. However, it occurs frequently enough that I recommend the option change for all triple modems being used for incoming calls. Be sure to let me know if you have any questions about or problems with this info. I hope it's of some use, bunky... --Lauren--