74HC4052 as a serial extension?

[abdullahseba]

Hi
Can I use a 74HC4052 as "extension lead"?
I have 2 serial devices that have an LCD and when connected to the serial port I need both to display the same thing. It also has a keypad and both need to send to the same port.
Its unlikely that both units will be used at the same time an even more unlikely that a button on each keypad will be pressed at exactly the same time.
I thought that muxes where used to more as a "switch" than a "hub" in networking terms but this sparkfun schematic seems to be what I want https://www.sparkfun.com/datasheets/Components/General/SerialMux-v10.pdf
Does this do what I want? Or is it a switch?
Thanks in advance.

[alm]

It will be a switch in that the UART on your microcontroller (?) will only be transmitting to and receiving from one of the serial devices at the same time. The difference to a switch in network terms is that the microcontroller will have to explicitly switch between the displays. So you have to change the MUX configuration (through the MUX_A/MUX_B lines) to select which display you want to talk to. Similar to the old manual KVM-switches where you had to press a button or turn a dial to select a computer.

[abdullahseba]

So

It will be a switch in that the UART on your microcontroller (?) will only be transmitting to and receiving from one of the serial devices at the same time. The difference to a switch in network terms is that the microcontroller will have to explicitly switch between the displays. So you have to change the MUX configuration (through the MUX_A/MUX_B lines) to select which display you want to talk to. Similar to the old manual KVM-switches where you had to press a button or turn a dial to select a computer.

So how do you switch between the devices in the circuit? I seen no other inputs to the micro in the schematic.

[alm]

You would connect one of the GPIOs to MUX_A or MUX_B. Two GPIOs if you want to control three or four devices. See the 74HC4052 datasheet for how the A and B pins relate to the 0/1/2/3 outputs. Whichever pin you do not connect to your micro will be pulled low by the 1 kOhm resistor, so connecting one of the inputs if sufficient if you only need to switch between two outputs.