Campbell Scientific CR23X Micrologger - Manual (Page 81)

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
6-3
6.2.1 ENABLING AND ADDRESSING
PERIPHERALS
While several peripherals may be connected in
parallel to the CS I/O port, the CR23X has only
one transmit line (pin 9) and one receive line (pin
4, Table 6.2-1). The CR23X 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.
6.2.1.1 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
6.2.5).
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 or SC929 interface.
The CR23X interprets a ring interrupt (Section
6.2.2) to come from a modem if the device
raises the CR23X's Ring line, and holds it high
until the CR23X raises the ME line. Only one
modem/ terminal may be connected to the
CR23X.
Print Peripherals are defined as peripherals
which have an asynchronous serial
communications port used to RECEIVE data
transferred by the CR23X. 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 CS I/O connector. Use of the SDE line as an
enable line maintains CR23X 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.
6.2.1.2 ADDRESSED PERIPHERALS
The CR23X 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 6.2.1.1); an SD
is enabled by an address synchronously clocked
from the CR23X (Section 6.2.5).
Up to 16 SDs may be addressed by the CR23X.
Unlike an enabled peripheral, the CR23X
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 CR23X.
Synchronously addressed peripherals include
Storage Modules, SDC99 Synchronous Device
Interface (SDC99), and RF95 RF Modem when
configured as a synchronous device. The SDC99
interface is used to address peripherals which are
normally modem enabled (Figure 6.2-1).
6.2.2 RING INTERRUPTS
There are two peripherals that can raise the
CR23X's ring line; modems and the RF Modem
configured for synchronous device for
communication (RF-SDC). The RF-SDC is
used when the CR23X is installed at a
telephone to RF base station.
When the Ring line is raised, the processor is
interrupted, and the CR23X determines which
peripheral raised the Ring line through a process
of elimination (Figure 6.2-3). The CR23X raises
the CLK/HS line forcing all SDs to drop the ring
line. If the ring line is still high the peripheral is a
modem, and the ME line is raised. If the ring line
is low the CR23X addresses the Keyboard
Display and RF-SDC to determine which device
to service. (Section 6.2.5)
After the CR23X has determined which
peripheral raised the Ring line, the hierarchy is
as follows:
A modem which raises the Ring line will interrupt
and gain control of the CR23X. A ring from a
modem aborts data transfer to pin-enabled and
addressed peripherals.