Enabling And Addressing Peripherals; Hardware Enabled And Synchronously Addressed Peripherals - Campbell CR510 Operator's Manual

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
(ME)
MODEM
(COM200
RF95
SC32A)
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 CR510 has only
one transmit line (pin 9) and one receive line (pin
4, Table 6.1-1). The CR510 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 CR510 interprets a ring interrupt (Section
6.3) to come from a modem if the device raises
the CR510's Ring line, and holds it high until the
CR510 raises the ME line. Only one modem/
terminal may be connected to the CR510.
Print Peripherals are defined as peripherals
which have an asynchronous serial
communications port used to RECEIVE data
transferred by the CR510. In most cases the
6-2
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 CR510 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 CR510 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 CR510 (Section 6.6).
Up to 16 SDs may be addressed by the CR510.
Unlike an enabled peripheral, the CR510
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 CR510.