In SX Microcontrollers, SX/B Compiler and SX-Key Tool, robotworkshop wrote:

Hello Bean,

The legacy device is an older 680x based system with a single serial port.  I can easily send whatever I want to the serial port and it can easily control a digital I/O port which it can use to specify what serial device should be hearing what it has to say.  Adding an extra UART or trying to bit bang out the Serial data on another line would be much more complicated that just toggling an I/O line high or low to select the target device.  I had thought about just sending everything to the SX48 and let it forward on things not meant for it but the way things are falling into place it may be easier to keep everything on the host.  Besides, I think this may come up again and want to get this working as an alternate method of sharing a port.  It should also work for sharing other things too.

So, the Serial out from the host would go to pins 1 and 3 on the 4066, Pin 2 (4066) would go to the Serial in on target device #1, Pin 4 (4066) would go to the Serial in on target device #2 (sx48 in this case).  One digital line from the host would go pin 13 on the 4066.  That same control line would be connected to one of the inverters on a 74HC14 and then goto pin 5 on the 4066.  In theory it should only let the host talk to one of the serial target devices and the other will hear nothing.

This post isn't about if the Serial port should be shared in this example.  That's not the point.  It is more of a question that if it does need to be done, what is the best way to share the line and are there better choices than using a 4066 chip.  I've seen some examples on using a 74hc157 so that the host could selectively listen to two separate target devices but that was the opposite of what I wanted to do.

Anyway, if you know of any examples or urls that may reference something like this or have any suggestions let me know.

Best Regards,

Robert

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