Connecting multiple TX to a single RX

_panzerschreck_ · Joined: 06 Feb 2012 Posts: 6

Hello everybody,

I am planning to design a system with one control unit (PIC) and 8 slave units(8 PICs) and the communication will be established in two ways.

I am sending from control TX to slave RX's by a 3-to-8 line decoder to multiplex my TX signal and choose the correct receiver.

However I am having trouble to create the opposite. I only want to receive data from the pic that the controller unit desires. I tried 74HC151 8x1 MUX but could not get any success.

Is there any way to implement this with only ccs c side.

My best regards

FvM · Joined: 27 Aug 2008 Posts: 2337 Location: Germany

I don't see a reason why 74151 shouldn't work for logic level UART interface. A pure software solution is possible as well:
- define addresses for individual slaves and make them work after a selection command only.
- disable slave UART TX pins by default, enable it only for the selected device

This way RX and TX can be connected without multiplexers

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

To elaborate a bit more:
- When total wire length is less then 3 meters you could consider using I2C as it is faster and easier to implement.
- For the software UART solution there are many UARTS with an Address Detect Mode. Most PIC18 and few PIC16 processors have such an UART and can make software design a lot easier. More info on addressable UARTS in Microchip AN774: Asynchronous Communications with the PICmicro USART