Operator`s manual

SECTION 6. 9 PIN SERIAL INPUT/OUTPUT
6-2
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 Interface regulates the 12 volts to 6
volts to power the RC35 recorder. Only one
tape interface 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
port 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. It 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.g., two Storage Modules, Section 4.4.1);
all connected receive the same data.
6.3 INTERRUPTING DATA TRANSFER
TO STORAGE PERIPHERALS
Instruction 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 Instruction
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. If
the # key is pressed during data transfer, the
transfer is stopped and the display shows the
Final Storage location where the pointer
stopped.
Data transfer can be stopped as follows:
1. Printable ASCII - after every output array.
2. Binary - after every Final Storage location.
3. Tape - after every block (512 Final Storage
locations).
6.4 TELECOMMUNICATIONS - MODEM
PERIPHERALS
Any serial communication device which raises
the Ring line and holds it high until the ME line is
raised is a modem. The DC112 phone modem,
RF95 RF modem, MD9 Multi-Drop Interface,
and the SC32A RS232 interface 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 until the 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 not
shown while the 21X is in telecommunications.
Some modems are quite noisy when not on line;
it is possible for valid characters to appear in the
noise pattern. For this reason, the 21X counts
all the 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
serial communication between the 21X and
common computer equipment. If 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.