Modem/Terminal Peripherals; Synchronous Device Communication - Campbell Measurement and Control Module CR10 Operator's Manual

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
1. Comma delineated ASCII - after every 32
characters.
2. Printable ASCII - after every line.
3. Binary - after every 256 Final Storage locations.
4. Tape - after every block (512 Final Storage
locations).

6.5 MODEM/TERMINAL PERIPHERALS

The CR10 considers any device with an
asynchronous serial communications port
which raises the Ring line (and holds it high
until the ME line is raised) to be a modem
peripheral. Modem/terminals include Campbell
Scientific phone modems, and most computers,
terminals, and modems using the SC32A
Optically Isolated RS232 Interface.
When a modem raises the Ring line, the CR10
responds by raising the ME line. The CR10 must
then receive carriage returns until it can establish
baud rate. When the baud rate has been set, the
CR10 sends a carriage return, line feed, "*".
The ME line is held high until the CR10
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 (2
minutes in the Remote Keyboard State).
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 CR10 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.
6.6 SYNCHRONOUS DEVICE
COMMUNICATION
The CR10 differs from other Campbell Scientific
dataloggers by its ability to address
6-4
Synchronous Devices (SDs). SDs differ from
enabled peripherals (Section 6.2.1) in that they
are not enabled solely by a hardware line. An
SD is enabled by an address synchronously
clocked from the CR10. Up to 16 SDs may be
addressed by the CR10, requiring only three
pins of the 9-pin connector.
Synchronous Device Communication (SDC)
discussed here is for those peripherals which
connect to the 9-pin serial port. This should not
be confused with Synchronous Device for
Measurement (SDM) peripherals connected to
control ports 1, 2, and 3. (Although the
communication protocol for SDMs is very
similar, their addressing is independent of SDC
addresses and they do not have a ring line.)
SD STATES
The CR10 and the SDs use a combination of
the Ring, Clock Handshake (CLK/HS) and
Synchronous Device Enable (SDE) lines to
establish communication. The CR10 can put
the SDs into one of six states.
STATE 1, the SD Reset State
The CR10 forces the SDs to the reset/request
state by lowering the SDE and CLK/HS lines.
The SD cannot drive the CLK/HS or RXD lines
in State 1, however, it can raise the Ring line if
service is needed. The SD can never pull the
Ring low if a Modem/Terminal is holding it high.
Data on TXD is ignored by the SD.
STATE 2, the SD Addressing State
The CR10 places the SDs in the addressing
state by raising CLK/HS followed by or
simultaneously raising SDE (Figure 6.6-1).
TXD must be low while SDE and CLK/HS are
changing to the high state.