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SECTION
6.
9
PIN
SERIAL INPUT/OUTPUT
6.2
ENABLING PERIPHERALS
Several peripherals may
be
connected in parallel
to the 9-pin
port.
The 21X directs data
to
a
particular peripheral by raising the voltage on
a
specific pin dedicated to
the peripheral; the
peripheral
is
enabled when
the pin goes high.
Three pins are dedicated.to specific devices,
Tape Enable pin 8, Modem Enable pin 5, and
Print Enable pin
6.
Tape Enable (TE), pin 8, is raised to
12
volts to
power the
tape recorder. The SC92A or SC93A
Cassette
lnterface regulates the
12
volts
to
6
volts
to power the RC35
recorder.
Only one
tape
inbrtace
and recorder may be
connected
to
the
21X.
Modem Enable (ME), pin
5, is raised to enable
a modem
that has raised the ring
line.
Only one
modem/terminal may be connected to
the
21X.
Print Enable (PE), pin 6, is raised to enable a
Storage Module or other print
peripheral.
Print
peripherals are defined as peripherals which
have an asynchronous serial communications
pod used to RECEIVE data transferred by the
21X.
In
most cases
the peripheral
is
a printer,
but
could also be an on-line computer or
other
device. lt
is
possible
to have more than one
print peripheral connected to the 21X at one
time,
as long as they don't load down the TXD
line (e.9., two Storage Modules, Section 4.4.1);
allconnected receive the same data.
6.3
INTERRUPTING DATA TRANSFER
TO STORAGE PERIPHERALS
lnstruction 96 is used for on-line data transfer to
peripherals (Section
4.1).
Data
transfer
is
aborted when
a modem raises the Ring line and
the 21X
then enters Telecommunications
(Section 5,
6.4).
After the
21X exits
Telecommunications, data transfer to
the
peripheral is resumed
the next time lnstruction
96
is
executed, or, if activated
by
the *4 Mode,
at
the completion
of
the next active table.
The *8 and *9 Modes are used to position the
Memory Pointers, and
to manually initiate data
transfer
from Final Storage to a
peripheral.
lf
the
# key is pressed during data transfer, the
transfer
is
stopped and the display shows
the
Final Storage location where
the pointer
stopped.
6-2
Data transfer
can be stopped as follows:
Printable ASCII
-
after every output array.
Binary
-
after
every Final Storage location.
Tape
-
after every
block (512 Final Storage
locations).
6.4
TELECOMMUNICATIONS
.
MODEM
PERIPHERALS
Any
serialcommunication device which raises
the Ring line and holds it high
untilthe
ME
line
raised is
a modem. The DC112 phone modem,
RF95 RF modem, MD9 Multi-Drop Interface,
and
the SC32A RS232 inter{ace used with
computers or
terminals are modems.
When
a modem raises the Ring line, the 21X
responds by raising
the ME
line.
The
21X must
be sent
carriage returns until
it
sets
the baud
rate.
When the baud rate
is
set, the 21X sends
a
carriage return,
line
feed,
*.
The ME line is held high
untilthe 21X
receives
an
E
to exit
telecommunications. The ME
is
also lowered
if
a character is not received
after
40
seconds
in
the Telecommunications
Command State
or
147
seconds
in
the Remote
Keyboard
State.
The colon
in
21X display
is
shown while
the 21X is
in
telecommunications.
Some modems are
quite noisy when not
on
it is possible for valid characters
to appear
in
noise
pattern.
For
this reason, the 21X counts
allthe
invalid
characters it receives from the
time
it
answers
a ring and terminates
communication (lowers the ME line and returns
to
the "0 Mode) after receiving 150 invalid
characters.
6.5
INTERFACING WITH COMPUTERS,
TERMINALS, AND PRINTERS
This section deals with some
of
the basics
of
serialcommunication between the 21X and
common computer
equipment.
lf
you have
an
IBM
compatible PC,
the PC208 Datalogger
Support Software takes care of the software
protocol required
in
communicating with
the
21X.
This section
does not discuss modem
interfaces other than
the
SC32A.
Please refer
to
the PC208 and modem operator's manuals
for interfacing details on other modems.
1.
2.
3.
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