Campbell Scientific CR10X Measurement and Control System - Manual (Page 78)

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
6-2
FIGURE 6.2-1. Hardware Enabled and Synchronously Addressed Peripherals
6.2 ENABLING AND ADDRESSING
PERIPHERALS
While several peripherals may be connected in
parallel to the 9-pin port, the CR10X has only
one transmit line (pin 9) and one receive line (pin
4, Table 6.1-1). The CR10X selects a peripheral
in one of two ways: 1) A specific pin is dedicated
to that peripheral and the peripheral is enabled
when the pin goes high; we will call this pin-
enabled or simply enabled. 2) The peripheral is
addressed; the address is sent on pin 9, each bit
being synchronously clocked using pin 7. Pin 6
is set high while addressing.
6.2.1 PIN-ENABLED PERIPHERALS
Modem Enable (pin 5) is dedicated to a specific
device. Synchronous Device Enable (pin 6) can
either be used as a Print Enable or it can be
used to address Synchronous Devices (Section
6.6).
Modem Enable (ME), pin 5, is raised to enable
a modem that has raised the ring line.
Modem/terminal peripherals include Campbell
Scientific phone modems and computers or
terminals using the SC32A RS232 interface.
The CR10X interprets a ring interrupt (Section
6.3) to come from a modem if the device raises
the CR10X's Ring line, and holds it high until the
CR10X raises the ME line. Only one modem/
terminal may be connected to the CR10X.
Print Peripherals are defined as peripherals
which have an asynchronous serial
communications port used to RECEIVE data
transferred by the CR10X. In most cases the
print peripheral is a printer, but could also be an
on-line computer or other device.
Synchronous Device Enable (SDE), pin 6, may be
used to enable a print peripheral only when no
other addressable peripherals are connected to
the 9-pin connector. Use of the SDE line as an
enable line maintains CR10X compatibility with
printer-type peripherals which require a line to be
held high (Data Terminal Ready) in order to
receive data.
If output to both a print peripheral and an
addressable peripheral is necessary the SDC99
Synchronous Device Interface is required. With
the SDC99 the print peripheral functions as an
addressable peripheral. If the SDC99 is not
used, the print peripheral receives the address
and data sent to the addressed peripheral.
Synchronous addressing appears as garbage
characters on a print peripheral.
6.2.2 ADDRESSED PERIPHERALS
The CR10X has the ability to address
Synchronous Devices (SDs). SDs differ from
enabled peripherals in that they are not enabled
solely by a hardware line (Section 6.2.1); an SD is
enabled by an address synchronously clocked
from the CR10X (Section 6.6).
Up to 16 SDs may be addressed by the CR10X.
Unlike an enabled peripheral, the CR10X
establishes communication with an addressed
peripheral before data are transferred. During
data transfer an addressed peripheral uses pin
7 as a handshake line with the CR10X.