Modem Control Status (Register Al) - Zenith Z-100 Reference Manual

Table 8.14. Modem Control Status (Register AL)
BIT STATUS
CTS line has changed state.
DSR status has changed.
End of ringing pulse detector.
Carrier Detect (CD) signal has changed state.
Status of CTS line.
Status of DSR line.
Ringing indicator.
Carrier detect status.
Serial and Parallel Input/Output
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