Campbell CR23X, Operator'S Manual, Page: 83 / 374

SECTION 6. 9-PIN SERIAL INPUT/OUTPUT
6-5
to the address, however. State 2 ends when
the 8th bit is received by the SD.
SDs implemented with shift registers decode
the 4 most significant bits (bits 4, 5, 6, and 7) for
an address. Bit 0 is always logic high. Bits 1, 2,
and 3 are optional function selectors or
commands. Addresses established to date are
shown in Table 6.2-2 and are decoded with
respect to the TXD line.
TABLE 6.2-2. SD Addresses
B7 B6 B5 B4 B3 B2 B1 B0
VS1 0 1 1 0 X X X 1
SDC99 Printer 0 0 0 0 X X X 1
Storage Module 0 0 0 1 X X X 1
RF95 Modem 0 0 1 1 X X X 1
STATE 3 , the SD Active State
The SD addressed by State 2, enters State 3.
All other SDs enter State 4. An active SD
returns to State 1 by resetting itself, or by the
CR23X forcing it to reset.
Active SDs have different acknowledgment and
communication protocols. Once addressed, the
SD is free to use the CLK/HS, TXD, and RXD
lines according to its protocol with the CR23X.
The CR23X may also pulse the SDE line after
addressing, as long as the CLK/HS and SDE
are not low at the same time.
STATE 4 , the SD Inactive State
The SDs not addressed by State 2 enter State
4, if not able to reset themselves (e.g., SM192
Storage Module). Inactive SDs ignore data on
the TXD line and are not allowed to use the
CLK/HS or RXD lines. Inactive SDs may raise
the Ring line to request service.
STATE 5
State 5 is a branch from State 1 when the SDE
line is high and the CLK/HS line is low. The
SDs must drop the Ring line in this state. This
state is not used by SDs. The CR23X must
force the SDs back to the reset state from State
5 before addressing SDs.
STATE 6
State 6 is a branch from State 1, like State 5,
except the SDE line is low and the CLK/HS line
is high. The SDs must drop the Ring line in this
state.
6.2.6 MODEM/TERMINAL AND COMPUTER
REQUIREMENTS
The CR23X 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.
Modems include Campbell Scientific phone
modems, and most computers, terminals, and
modems using the SC32A Optically Isolated
RS-232 Interface.
FIGURE 6.2-4. Addressing Sequence for the RF Modem