2 rs-232 point-to-point mode, 3 rs-485 ttl differential signaling mode – INFICON STM-2XM 2-Channel Rate/Thickness Monitor User Manual
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STM-2XM Operating Manual
5.2.2 RS-232 Point-to-Point Mode
STM-2XM can be set to RS-232 point-to-point mode for a single host-slave
connection by selecting SMDP address 16 (0x10). Point-to-point mode can be set
to one of three baud rates (high-115200, medium-38400, low-9600) via the Comm
Protocol menu accessed from the System Settings menu (refer to
). This supports a three wire (transmit, receive, common ground)
interface that can be directly connected to most RS-232 ports of a computer or
controller. The protocol is standard 10 bit (1 start bit, 8 data bits, 1 stop bit) (see
).
5.2.3 RS-485 TTL Differential Signaling Mode
RS-485 TTL differential signaling mode is selected by SMDP address values 17
through 254. In TTL differential signaling mode, two wires are time-shared
(half-duplex) between a master and 1 to N slaves. Slaves monitor the state of the
A/B differential signals, looking for the master to a frame
(start-data-stop-start-data-stop-etc). When a slave receives a frame that is
addressed for it (address byte value 17 to 254), the slave will drive the A/B wire pair
differentially with its own reply frame, which the master (and all other slaves) will
see. Since the reply has an address byte embedded in it, other slaves will ignore
the reply. The host will decode and verify (via checksum) the reply. If acceptable,
the reply will be used by the master.
The RS-232 pin assignments for the PN 783-506-000 cable (see
) are
Pin 2 (TXD), Pin 3 (RXD), and Pin 5 (Signal GND). The cable wiring is
straight-through (not null modem).
When using the PN 783-560-000 cable for RS-485 communication, the pin
assignments are Pin 2 - Green (inverting signal), Pin 3 - Red (non-inverting signal),
and Pin 5 (Signal GND). The RS-485 / TIA-485 standard does not specify pin
assignments, so a modification may be needed at the cable end connected to the
RS-485 card. Refer to the RS-485 card operating manual to determine which pins
are inverting and non-inverting.
NOTE: If the inverting and non-inverting signal connections to the RS-485 card are
reversed, the RS-485 link will not communicate; however, STM-2XM and
the RS-485 card will not be damaged.