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The gated XMIT CLK that clocks the
transmitter is selected by the BAUD rate
select logic and is 16 times the baud rate.
In read back test operation (factory only) the
contents of the memory buffer (CBUFn) may
be accepted for transmission in the same
manner as data on the KCn lines.
4.2.8 Interface Logic Control
The interface control logic controls the Clear-
to-Send and Request-to-Send exchanges
between the modem or computer and the
ADM 5. Either a code-turnaround or a reverse
channel system may be used to transfer
control from one end of the communication
line to the other. Switches adapt the logic to
interface with type 103 or 202 modems or to
operate under internal control.
CLR TO SEND (high) permits data
transmission logic to produce XMIT CLK,
sending data from the ADM 5.
If
CLR TO
SEND falls when a byte is being transmitted,
the transmit clock is maintained until the
byte has been completed, then falls to shut off
the clock and return the line to the marking
state. REQ TO SEND (RTS) may be
controlled in one of five ways as follows:
a. RTS may originate at an extension port.
b. If switches 202, 103, and LOCAL are all
open, RTS remains low all the time.
c.
If
only switch 103 is closed, RTS remains
high all the time.
d.
If
only the LOCAL switch is closed, RTS
rises to transmit each character, and
falls when the character has been shifted
out of the ADM 5.
e. If only the 202 switch is closed, RTS may
be controlled through the ADM 5
interface in either code turnaround, or
reverse-channel operation.
4.2.8.1 Code Turnaround Control
Either an ETX or an EOT code may be
selected, depending upon the position o( the
ETX and EOT switches, to initiate
turnaround operation. When the selected code
appears in the input data, LATCHED CODE
is set. When CARRIER DETECT falls
DP319
4-7
(figure 4-15) indicating that the remote end
of the line has dropped, RTS is set.
RTS is reset when ETX or EOT is again
decoded and the logic switches to the receive
mode. Following a turnaround command, no
further command will be recognized for
approximately 250 milliseconds. This
interval gives the modem time to propagate
its signals. The interval is timed-out by two
flip-flops, a couunter, and the signal SBEN
that controls resetting of RTS.
4.2.8.2 Reverse Channel Control
During reverse channel operation, RTS is
controlled by SEC RECV DATA (SB) and
CARRIER DETECT (CF) from the modem.
When SB goes low, RTS is unconditionally
reset (figure 4-16)switching the interface to
receive data. In normal reverse channel
receive operation, CF is high at this time,
causing SEC XMIT DATA to rise.
When the remote end of the line raises SB and
then drops its RTS (and CF), the ADM 5 will
activate its RTS. The ADM 5 will then ignore
further commands for a 250 millisecond
period while the modem propagates its
signals.
4.2.9 CRT Display Monitor
The CRT display monitor employed in the
ADM 5 is a solid-state unit for use in
industrial and commercial installations
where reliability and high-quality video
reproduction are desired.
The monitor features printed circuit board
construction for reliability and uniformity.
All circuits of the monitor are transistorized.
Several different monitor assemblies have
been utilized in the ADM 5. For details on
operation, layout, and parts information refer
to Section 6 which includes the various
assemblies.
4.2.10 Power Supplies
AC power is applied to the transformer
through the ON/OFF switch on the rear of
the ADM 5. The different stepped down AC
voltages are connected to the main circuit
board connectors. Recetifiers, filter
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