User`s manual
Table 3-8 (Cont)
Control Status
Register Bit
A~ignments
Bit(s) Designation
Function
Read/Write
07
DONE
Set to one whenever a transition occurs on a
Read or Write
status line (RING,
CO, CS, DSR) from an
enabled modem during the modem scanning
process,
as
initiated by Scan
En
(CSR bit 5).
When Done
is
set to one, the scan stops and the
status transition(s) are
se.t
in
CSR bits
12-15.
The line number
of
the modem with the
new
status
is
in
CSR bits
0-3,
and the current states
of
that modem's status lines are reflected
in
LSR
bits
4-7.
Cleared by Initialize and Clr Scan (CSR
bit 11).
08 STEP
When
set
to
1, causes the line number
in
CSR bits
0-3
to
be
incremented by
1.
If a status transition
is
detected for the new line, Done (CSR bit 7)
is
set to
1.
Done does not inhibit Step. This bit
is
used principally for maintenance and requires
1 .2 microseconds ± 1
0%
to
execute. This bit
is
write ones only.
09 (Maintenance )
10
CLEARMUX
Clears bits
4-7
of
the LSR (RS, Term Rdy,
NS,
Write ones
tine
En) for all lines when set to 1. This bit
is
write ones only.
11
CLR SCAN
Clears
bits
0-3,5,6,
7,9,
and
12-15
of
the
CSR
Write ones
when set to 1, and clears
MCU
"Scan Memory" in
18.8 microseconds ±
10%.
(The
MCU
detects modem status transitions by
storing the conditions
of
the several modems'
status lines in Scan Memory, then continuously
comparing the updated status conditions with
the previous status conditions during the modem
scanning process. Thus, if Scan
En
(CSR bit 5)
is set to 1 following a Clear Scan and the interrupt
mode
is
set, an interrupt will occur for all modems
which have
ON status lines (DSR, CS, CO, RING),
as
these will appear
as
OFF to ON transitions to
the
MCU.)
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