PDP11 PeripheralsHbk 1972 - Trailing-Edge

used by the ACU. It allows the program·
mer to test the ACU to see if the last call
was successfully terminated before he
tries to use it for the next one (Read only).
11·8 Digit Bits (NBl·4) These four bits are control leads to the
ACU. These low order bits of the second
byte make up the BCD digit to be dialed.
Since th,e high·order four are read only. it
does not matter what is in them during a
load, and the programmer may use them
as he wishes. In MA1NT mode, these bits
are used t9 drive the four control lines that
can cause interrupts. See bit 03 for de·
scription (Read /Write).
7 DON E This bit is set to indicate that the ACU is
done with the previously requested action
and ready to accept new data, usually the
next digit in a sequence to be dialed.
The conditions that set DONE are listed
(CRQ must be a one):
1. Transition of PND to one (after CRQ set
or previous DPR set).
2. Transition of DSS to one (after last DPR
or EON).
3. Transition of ACR to one (if timeout er·
ror .. anytime).
4. Transition of DLO to one (if power
switched off) (Read/Write)
6 Interrupt Enable (INTENB) This bit allows the setting of done to cause
an interrupt if ·the master enable bit (bit
02 line # 1 of a system unit) is set
(Read /Write).
5 Data Set Status (FDSS) Control lead from ACU. This is a state·
ment by the ACU that the called party has
answered and that the associated data set
now has control of the line. It is accompa·
nied by the setting of DONE to obtain an
interrupt. It remains set until after the end
of the call (Or until the data terminal
ready lead to the associated modem is
dropped which then drops FDSS).
If the associated modem answers a call
while the dialer is in use (CRQ = 1), then
DSS will be enabled and DONE set. If interrupt
Enable is set there will be an interrupt
(Read only).
4 Present Next Digit (FPND) Control lead from the ACU. This is a
request by the ACU for the program to
load another digit during dialing. It is ac·
companied by the setting of DONE to ob·
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