3708 Problems Related To Cables Or Equipment - IBM 3708 Planning And Installation

3708 Problems Related to Cables or Equipment
. An incorrectly wired cable or incorrectly operating eqUipment (modem, modem
eliminator, host, or end-user device) that is connected directly to a 3708 port can
prevent the 3708 from operating. This problem occurs if the cable or equipment
applies a signal to one of the following port connector pins: 2,4, 12, 14, 18, 20, 21,
23, or 24.
Example 1: ROLM DTI users must ensure that the DTI is configured correctly and
that the DTI switch SI-1 is set to OPEN (No). Otherwise, the DTI applies a signal
to pin 20 of the 3708, which may prevent the 3708 from turning on.
Recommended switch setting for the ROLM DTI are as follows:
Switch #1 (SI):
Forced DTR On
Carrier Detect and CTS Display
Audible Signal Enabled
Terminal/Computer" Option
Originate Answer/Answer
Off Hook Control Switch
Slide Switch (S3):
Modem/Terminal Option
OPEN (No)
Either OPEN or CLOSED
Either OPEN or CLOSED
OPEN (TERMINAL)
CLOSED (ANSWER)
OPEN
TERMINAL
Example 2: IBM 5841 users must set configuration switch 8 (Data Set Ready
option) to OFF. Setting this switch to ON causes the modem to hold Data Set
Ready high (active) at all times. If the 3708 port is switched, and Data Set Ready is
active all the time, the 3708 does not enable the port.
To avoid signals on pins 2, 4, 12, 14, 18, 20, 21, 23, or 24, it is recommended that
25-pin conductor cables not be used.
Example
3: Some synchronous modems and modem sharing devices do not hold the
TXD line at a MARK level after RTS is dropped. This prevents devices on the
same multi-drop line from communicating with the host. The problem occurs when
the line is configured for NRZI data encoding.
The problem can be prevented by doing one of the following:
• Configure the modem/modem sharing device to hold the TXD line at a MARK
level when RTS is dropped
• Configure the line for NRZ data encoding.
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3708 Planning and Install/ltion