IBM pSeries 670, Service Manual

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Xon/Xoff Modems
Some early modems assume software flow control (Xon/Xoff) between the computer and the modem.
Modems with this design send extra characters during and after the transmitted data. The service
processor cannot accept these extra characters. If your configuration includes such a modem, your
functional results may be unpredictable.
The sample modem configuration files included in this appendix do not support these modems, so custom
configuration files are necessary. Anchor Automation 2400E is an example of such a modem.
If you experience unexplainable performance problems that may be due to Xon/Xoff characters, it is
recommended that you upgrade your modem.
Ring Detection
Most modems produce an interrupt request each time they detect a ring signal. Some modems generate
an interrupt only on the first ring signal that they receive. AT&T DataPort 2001 is an example of such a
modem.
The service processor uses the ring interrupt request to count the number of rings when Ring Indicate
Power-On (RIPO) is enabled. If your modem produces an interrupt on only the first ring, set Ring Indicate
Power-On to start on the first ring. Otherwise, you can choose to start Ring Indicate Power-On on any ring
count.
Terminal Emulators
The service processor is compatible with simple ASCII terminals, and therefore compatible with most
emulators. When a remote session is handed off from the service processor to the operating system,
agreement between terminal emulators becomes important.
The server’s operating system will have some built-in terminal emulators. You may also have a
commercially available terminal emulation. It is important that the local and host computers select the
same or compatible terminal emulators so that the key assignments and responses match, ensuring
successful communications and control.
For best formatting, choose line wrap in your terminal emulator setup.
Recovery Procedures
Situations such as line noises and power surges can sometimes cause your modem to enter an undefined
state. When it is being used for dial-in, dial-out or ring indicate power-on, your modem is initialized each
time one of these actions is expected. If one of these environmental conditions occur after your modem
has been initialized, it might be necessary to recover your modem to a known state.
If your modem communicates correctly with remote users, it is probably in control. It may be wise to
occasionally change some of the functional settings and then change them back, just for the sense of
security that the modem is communicating, and to ensure it has been initialized recently.
If your system is particularly difficult to access physically, another strategy is to protect it with an
Uninterruptible Power Source (UPS) and a phone-line surge protector.
In case recovery becomes necessary, shut down your system using established procedures. Disconnect
the power cable and press the power button to drain capacitance while power is disconnected. Disconnect
and reconnect modem power, and then reconnect system power to completely reinitialize your system.
Appendix D. Modem Configurations
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