Campbell Scientific CR7 Measurement and Control System - Manual (Page 64)

SECTION 6. 9 PIN SERIAL INPUT/OUTPUT
6-2
6.2 ENABLING PERIPHERALS
Several peripherals may be connected in
parallel to the CS I/O 9-pin port. The CR7
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. Two pins are dedicated to
specific devices Modem Enable pin 5 and Print
Enable pin 6.
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 CR7.
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
CR7. 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 CR7 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 CR7 then enters Telecommunications
(Section 5, 6.4). After the CR7 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.
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 CSI field modem
(DC112, COM200, COM100, or DC1765), 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 CR7
responds by raising the ME line. The CR7 must
be sent carriage returns until it sets the baud
rate. When the baud rate is set, the CR7 sends
a carriage return, line feed, *.
The ME line is held high until the CR7 receives
an E to exit telecommunications or until a time
limit expires without receiving a character. The
colon in CR7 display is not shown while the
CR7 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 CR7
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 CR7 and
common computer equipment. If you have an
IBM compatible PC, the PC208(W) Datalogger
Support Software takes care of the software
protocol required in communicating with the
CR7. This section does not discuss modem
interfaces other than the SC32A. Please refer
to the PC208 software and modem operator's
manuals for interfacing details on other
modems.