3.1 SETTING THE DCE/DTE SWITCH
For your convenience, the Model 1004A has an externally
accessible DCE/DTE switch. If the device connected to the Model
1004A is a modem or multiplexer (or is wired like one), set the switch to
“DTE”. This setting causes the Model 1004A to behave like Data
Terminal Equipment and transmit data on pin 2. If the device
connected to the Model 1004A is a PC, terminal or host computer (or is
wired like one), set the switch to “DCE”. This setting causes the Model
1004A to behave like Data Communications Equipment and transmit
data on pin 3.
3.2 DIP SWITCH CONFIGURATION
The eight switches on switch set S1 (see Figure 3, above)
configure the Model 1004A for echo mode, carrier control method,
RTS/CTS delay, “transmit off” impedance, receive impedance, and 2-
wire/4-wire operation. These switches are located
internally on the
Model 1004A's PC board. To access switch set S1, use a small flat
blade screwdriver to pop open the Model 1004A's case as shown in
Figure 4, below.
5
3.3 DIP SWITCH SETTINGS
All possible settings for the Model 1004A’s configuration switches
are presented in the table below. Following the table is a detailed
description of each switch function. If you have additional questions,
contact Technical Support at (301) 975-1000.
*Note: Switches S1-1 & S1-2 should be switched simultaneously.
Switches S1-7 & S1-8 should also be switched simultaneously.
S1-1 and S1-2: “Transmit Off” Impedance
Switches S1-1 and S1-2 are set together to determine whether the
receiving device “sees” the impedance of the Model 1004A’s transmitter
as being “high” or “intermediate” when the transmitter is turned off. The
“intermediate” setting is useful in half-duplex environments where the
receiving device does not respond well to the “high” setting.
S1-1
S1-2
Setting
On
On
Intermediate Impedance
Off
Off
High Impedance
S1-3: RTS/CTS Delay
The setting for switch S1-3 determines the amount of delay
between the time the Model 1004A “sees” RTS and when it sends CTS.
Note: RTS/CTS Delay setting should be based upon transmission
timing.
S1-3
Setting
On
8 mSec
Off
no delay
S1-4: Echo Mode
6
S1 SUMMARY TABLE
Position
Function
Factory Default
S1-1*
“Transmit Off” Impedance
Off
S1-2*
“Transmit Off” Impedance
Off
S1-3
RTS/CTS Delay
On
8 msec
S1-4
“ECHO” Mode
Off
Echo Off
S1-5
Carrier Control
Off
Constantly On
S1-6
Receive Impedance
On
120 Ohm
S1-7*
2-Wire/4-Wire
Off
S1-8*
2-Wire/4-Wire
Off
High Z
4-Wire
}
}
Figure 4. Opening the Model 1004A's plastic case with a small screwdriver
Figure 3. Close-up of DIP switch showing “ON” and “OFF” positions
1
2
3
4
5
6
7
8
ON
OFF
ON
