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7. Must the parallel ICAO altitude data be connected to use the serial data?
No, the serial data output is completely independent of the parallel data output. However, power
must be supplied to the Digitizer through the ICAO altitude data connector.
8. How many devices may be driven off of the RS232 output?
One device may be driven off each serial output. The SSD120-(XX)N-RS5 Digitizer provides five
RS232 outputs, so five RS232 receiving devices may be driven off of each Digitizer.
9. Can the Digitizer transmit two different serial data protocol messages at the same time?
Yes. The five digitizer RS232 ports are divided into group A (TxD1, TxD2, TxD3) and group B
(TxD4 & 5.) The Digitizer may be configured via the serial port and an IBM compatible PC to
specify the data protocol to be transmitted on each serial output group. See §4.6.
10. What is the maximum length of an RS232C wiring harness?
25 feet.
11. I have connected the serial data from the digitizer to my GPS device, why does the GPS display a "No
Pressure Altitude" message?
There are several possible problem sources.
Electrical Ground Imbalance
RS232 operates in an "unbalanced" (single-ended) transmission method; where the receiving
device monitors the difference between the signal voltage and a common ground. If a significant
difference in electrical ground potential between the Digitizer and the receiving device exists, then
the RS232 signal levels may be adversely affected. Verify the digitizer and receiving device
electrical grounds are referenced together by connecting one of the ground pins on the Digitizer
RS232 connector to the receiving device's ground.
Receiving Device Configuration
The receiving device is looking for a specific message at a specific baud rate and parity. These
messages, baud rates and parity vary from manufacturer to manufacturer. A mismatch on any
one of these items will cause a communication failure. In addition, many devices are capable of
software configuration to accept RS232 data on different connector pins. Verify the following:
a. Digitizer data is routed to the correct connector pin on the receiving device.
b. The receiving device is software configured to accept data on that connector pin.
c. The receiving device is software configured to accept the correct message protocol at
the correct baud rate and parity.
d. The Digitizer is transmitting the same message, baud rate and parity as configured in
item c above.
12. How can I verify the RS232 data message, baud rate and parity transmitted from the Digitizer?
a. Use the Trans-Cal ATS-400 Test Set to display the RS232 data.
b. Substitute the Trans-Cal ADS-100 for the altitude encoder to simulate the serial data
transmission.
c. Use a PC with an open RS232 port and serial data capture software. Some possible software
solutions include: HYPER TERMINAL (Windows® 95 & 98 & XP), SOFTWARE WEDGE™,
PROCOMM™, VERSATERM™.
d. Use a dedicated serial data test box such as the BLACK BOX™ RS232 MONITOR.
e. An oscilloscope may be used to view the 9Vdc square wave transmitted about 2/second.
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