M
IDIAN
E
LECTRONICS
I
NCORPORATED
P
AGE
8
TDM-1 v 1.0
5-12-00
places the cursor at the beginning of the line. To move to the
next line, a Line Feed (LF) character must be sent with the CR
character to go to a new line. Most terminal programs can do
this for you. Please refer to the instructions for your dumb
terminal for more information.
I am using the TDM-1 menu system with my dumb
terminal and a blank line appears after each line of the
menu and now I cannot see all of the options. What is
causing this?
The TDM-1 automatically places a carriage return and a line
feed (see above) at the end of each line so that the menu
options will not type over themselves on the same line. Your
terminal is itself adding a line feed for each carriage return
character it receives. This is typically a configurable option on
a dumb terminal. Please refer to the instructions for your
dumb terminal for more information.
Can I transfer data files between computers with the
TDM-1?
Yes, the TDM-1 will support straight ASCII or binary file
transfers (uploads and downloads). The TDM-1 will generally
not
support file transfer protocols such as XMODEM,
YMODEM, KERMIT, etc. This is because the TDM-1 was
designed to accommodate 2-way radios and thus incorporates
PTT key-up delay, hang time, etc. These delays interfere with
the normal handshake of these full-duplex protocols.
Why are there errors in the data?
There are many possible causes for errors in data transmitted
over the air. These can range from a weak signal to outright
interference. The V.23 protocol does not implement any error
detection or correction. If you are seeing frequent data errors
and have a strong signal, you may need to adjust the
TX and
RX level
pots. You will need to open the DB-25 shell to make
these adjustments. See the installation page for details.
Why are there extraneous characters at the end of each
transmission?
The squelch tail heard on some radios at the end of a
transmission is often the cause of extraneous data. Try using
PL/DPL reverse burst on your radio to eliminate squelch tail.
Other possibilities include ANI signaling, voice talk-off, etc.
I connected my TDM-1 to a terminal and all I see is the
word TEST printing over and over again? What do I do?
The TDM-1 performs an EEPROM checksum test upon
power-up. This is done to verify the integrity of the
programmed parameters stored in EEPROM. Should this test
fail, the unit will repeatedly send the message TEST to the
DTE. To cancel the test mode and restore factory defaults,
send data from the DTE to the modem while the TEST
message is printing (eg. press any key). If this does not
restore operation, contact Midian for diagnostic proc edures.
4. ACRONYMS
This section is provided to clarify certain acronyms used in
this manual.
COR
This old radio term stands for Carrier Operated
Relay. For the purpose of this manual, this refers to
any signal which changes state when a radio detects
an RF carrier. Also known as Carrier Operated
Switch (COS).
CTS
Clear to Send. An RS-232 signal from a DCE to a
DTE used to control the flow of data from the DTE
(see definition of DTE below).
DCE
Data Communications Equipment (see DTE).
DTE
Data Terminal Equipment. For the purpose of this
manual, this is any device connected to the RS-232
port of the TDM-1. The TDM-1 can connect to any
device with an RS-232 port configured as a DTE.
This includes PC’s, laptop computers, handheld
terminals, dumb terminals, data terminals, GPS
modules, etc.
Historically,
DTE
refers to a dumb computer
terminal with an RS-232 port that can be connected
to a modem. A modem such as the TDM-1 is
considered to be Data Communications Equipment
(DCE).
Sometimes bar-code scanners and GPS modules
are configured as a DCE. If it is desired to connect
this modem to a device configured as a DCE, a null
modem will be required.
EEPROM
Electrically Erasable Programmable Read Only
Memory. This is a type of computer memory.
EEPROM retains the data stored in it for many
years, even if power is not applied. The TDM-1
employs EEPROM to store the user programmable
parameters such as Key-up delay. The EEPROM
may be re-programmed several thousand times.
TYPICAL NULL MODEM CONFIGURATION
DB25 PIN PIN
DB25
2 TX ------------------ RX 3
3 RX ------------------ TX 2
5 CTS ------------------ RTS 4
4 RTS ------------------ CTS 5
6 DSR ----------------+- CD 8
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