Thta's a clever idea. That would allow you to use the single hardware
UART for multiple devices.
Casually looking at the spec sheet... It looks like you will have to
have a VDD and VEE that are beyond the RS232 levels you are switching.
Do you have "REAL" RS232 signals? COM1 of the BasicX is 0-5V only,
it? The serial LCD is probably out output only. But the GPS and PC are
probably +/- volatges. You can measure the RS232 voltages to see what
voltages these devices are using.
If they are lower than a +/- 9, then you may be able to use a MAX232
type chip as your level translator (assuming you are using the software
UART) and as a +/- power supply. (I think the MAX232 chips generate +/-
9V) Otherwise you may need to supply an external +/- 12V or +/- 15V
supply. Then just drive the two address lines lines from BX-24 outputs.
I say this because the spec sheet says:
> Control of analog signals up to 20VP-P can be
achieved by digital
> signal amplitudes of 4.5V to 20V (if VDD-VSS = 3V, a
> VDD-VEE of up to 13V can be controlled; for VDD-VEE level
> differences above 13V, a VDD-VSS of at least 4.5V is
> required). For example, if VDD = +4.5V, VSS = 0V, and
> VEE = -13.5V, analog signals from -13.5V to +4.5V can be
> controlled by digital inputs of 0V to 5V.
This is from the Texas Instruments CD4052 data sheet. The 74hc4052 looks
like it only goes to +/- 5V instead of +/- 20V.
So I think if you use a CD4052 with a VDD of +12V and a VEE of -12V and
VSS is ground, then I think it will work with most "Modern" RS232
devices you hook up.
But I recommend you breadboard this and try it before connecting your
BX-24. So you don't blow it up. :-)
I built a 4 channel serial multiplexor using RS232 convertors and TTL
multiplexors. So every channel had RS232 convertors and the multiplexing
was at the TTL levels. I used the DTR and RTS lines (or whichever lines
were outputs) on the mater to select the channel. It was way too many
parts and way too much wiring.
PS: You may need pullup/pulldown resistors for a deselected channel. So
it doesn't receive constant input data. On the RS232 side I think you
need to pull down to your negative supply. But your devices may already
have these built it.
> Message: 1
> Date: Sat, 23 Apr 2005 13:43:25 -0400
> From: "Vic Fraenckel" <victorf@vict...>
> Subject: 4 channel multiplexer
> I have a need to distribute a single 3 wire RS232 to one of four seperate
> devices depending upon certain conditions in application processor. I may
> want to talk to a serial LCD, or a PC or a GPS. I would only need to talk
> one at a time however. I have been looking at a 4052 Dual 4 channel
> multiplexer to get the job done. The RS232 RXD line would go to one input
> (1Z) and the TXD line to the other input (2Z) some steering logic on the
> S0-S1 lindes determine which of the Y outputs would get the output from
> section, i.e. RXD would go to 1Y1, 1Y2, 1Y3 or 1Y4 and TXD to 2Y1, 2Y2,
> 2Y3, 2Y4 depending on the values on S0-S1.
> Is this a viable solution? If not why and what might be doable?
> Victor Fraenckel - The Windman
> victorf ATSIGN windreader DOTcom
> Home of the WindReader Electronic Theodolite
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