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Altek Dual Channel Multiplexer Altek Dual Channel Multiplexer

System Setup

Break the data link between the terminal and computer. A convienient place to do this is often behind the terminal where the unit is to be used.

Connect the computer to the Host connector. Connect the terminal to the Terminal connector.

Connect the multiplexor to a suitable power unit. (9 volts DC. Power Jack with 2.5 mm center pin. The pin polarity is positive)

Test the terminal keyboard to make sure it can still communicate with the computer. If it does not then the most likely reason is the data lines 2 and 3 are reversed. This can be corrected by throwing the switch inside the Mux. Remove the four screws and lift the lid. Change the position of the slide switch located close to the power connector. Replace the lid taking care that the hole in the case matches the power connector.

After you have established the terminal is working normally with the Mux in circuit connect your peripheral to either of the DB9 connectors. Data coming from the device should now appear on the terminal screen. If it does not then check that the peripheral outputs its data on pin 2 and that any RS232 handshake requirements are met by appropriate programming. In general it is usually best to operate the RS232 peripheral without handshaking.


The AC55 AC56 and AC57 have identical features but are set up in the factory in different configurations to suit different circumstances.

The standard model is the AC55. The AC56 and AC57 have alternative special configurations to suit particular customers needs. If you need a special pinout or configuration please let us know we can configure for your special needs at no additional cost prior to despatch. There is no minimum order for this.

AC55 The most popular model with a standard pinout. The AC55 works best with virtually all RS232 peripherals produced today. Choose this model unless you are clear you need a different configuration. Configuration
AC56 This is similar to the AC55 except pin 9 on each input is open circuit. It was our standard configuration prior to June 2004. If you used this model in the past and it worked for you then choose it again. Configuration
AC57 This is a special purpose pinout. Produced for a customer who required a special pinout to suit a particular brand of Mag Stripe reader attached to input 2. Configuration

Hardware features

DB25 Connectors & Data Direction Switch

There are two 25 way Dee connectors, male and female. The gender has been chosen so that it is easy to remove the multiplexor from the circuit simple by interconnecting the cables. Thus easing maintenance and restructuring operations. The Male connector should be connected to the Host computer. The Female to the Terminal.

All pins of each DB25 connector are interconnected with the exception of pins 2 and 3. Pin 7 is connected to ground. The direction of the data on pins 2 and 3 is controlled by a switch inside the unit. All other data lines are bidirectional.

Data Direction Switch

Switch away from the Power socket(default)...
Pins 2 interconnected. Data injected to pin 3 circuit.
Switch toward the Power socket...
Pins 3 interconnected. Data injected to pin 2 circuit.

Jumper links

There are two jumper links inside the Multiplexor one for each input channel. They provide the ability to isolate the data input pin of the peripheral device. For most configurations the link is open (Peripheral Data input open circuit).


Many peripherals which act mainly as a data source (Barcode Scanner, Magstripe Reader, Weighing Scales etc) are able to be programmed by sending it special programming codes. When used with a multoiplexer all data comming back from the computer to be displayed on the terminal will be 'seen' by the peripheral. This data is essentially random and from experience we have found it will sometimes accidentally cause the peripheral to be reprogrammed. This can be a difficult fault to diagnose. Opening the link isolates the peripheral input and thus avoids the problem. by using a jumper link the user can make the connection in the few cases it is necessary for correct operation. Multiplexer main page
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