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CiM-550 IP Enabled Satellite Modem
Theory of Operation
6.3 EIA-232 O
The CiM-550 supports asynchronous EIA-232 in addition to synchronous EIA-232
formats. This is useful, for example, in connecting two computers together, via their
serial ports, at opposite ends of a satellite link. There are, however, some restrictions and
limitations when using this mode, and the user may have to experiment a little in order to
get reliable communication.
6.3.1 ASYNC EIA-232 S
Maximum operating baud rate:
Additional data overhead required:
Maximum allowable baud rate
tolerance:
Character formats supported:
Flow control:
Handshaking line supported:
Connectivity required:
6.3.2 S
ETUP
The setup required for this mode is remarkably simple. Select EIA-232 as the interface
type, and then select the required baud rate for both transmit and receive data rates.
Detection of the asynchronous mode is fully automatic. If no clock is detected,
asynchronous mode is assumed, and the internal circuitry is switched accordingly. The
settings for both Tx and Rx clocking are irrelevant - the selected clocking options are
ignored, and the internal clock circuitry is reconfigured for this 'special' mode.
6.3.2.1 B
R
AUD
ATE
When connecting devices where the baud rate is not within the tolerance of +/- 600ppm,
the Tx FIFO and Rx Buffer will occasionally underflow or overflow, causing characters
to be lost. To avoid this, while the external device is connected, and transmitting data,
connect a frequency counter to pin 15 of the rear panel Data Connector (the 25 pin 'D'
type female). Measure the frequency, then set the transmit frequency to be equal to this
value on the local modem, and set the receive frequency to this value at the other end of
the link. If a frequency counter is not available, 10 minutes of trial and error will be an
adequate substitute. Set the modem to an IF loop, and then try changing the baud rate by
approximately 500 ppm at a time. At 9600 baud, this equates to either 9605 or 9595 baud,
with further increments of 5 bps. If changing the baud rate in a positive direction results
in more frequent buffer and/or FIFO slips, then move it in the opposite direction. Do this
until the slips are eliminated.
PERATION
PECIFICATIONS
A
CCURACY
57.6 kbaud (QPSK and OQPSK)
28.8 kbaud (BPSK)
Zero. A 9.6 kbaud connection uses a 9.6 kbps carrier.
+/- 600 ppm
Any, except those using 1.5 stop bits (see note below)
None
Data Carrier Detect (DCD)
Rx data, Tx Data and Ground (DCD optional)
83
Rev. 2
CD/CIM550.IOM
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