To reduce costs, many schools install a Serial Multiplexer to allow many Apples to share an Imagewriter. The multiplexer scans each computer by sampling a signal called "Data Set Ready" or DSR from the Super Serial Card in each IIe.
The nature of the SSC causes a modem nullifier to map this signal to DTR, "Data Terminal Ready." Normally this signal is not turned off by the computer since other equipment, like a modem, requires this signal to remain on. In this configuration the Serial Multiplexer stops scanning and hangs if the signal is not dropped. A simple POKE in BASIC releases the line.
The general form is: POKE 49050+256*Slot,1
Example
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Most systems have the SSC in slot 1, so the command is:
POKE 49306,0
Article Change History:
16 Dec 1996 - Reviewed for technical accuracy, revised formatting.