74HC4052 Alternative?

You have many choices available. The number of choices is greater if you are switching the TxD and RxD lines at the logic level voltages right at the microcontroller. If on the other hand the switching is being done on the other side of an RS232 transceiver then your choice of available switch parts becomes a lot more limited.

You could look at the MAX303 switching element. It offers two SPDT configured switches that looks like it it would fit your application directly. This part could be designed in to support the switching on either side of the RS232 transceivers. See here:

Another choice you could consider is to toss the mux/switch idea all together (and as long as both of your ports already require level translators) you could look at a part similar to the ADM211 (there are many others too) that has a tri-state enable pin. These essentially allow you to tri-state bus multi-drop the microcontroller serial port lines to multiple RS232 ports.

- mkaras

Thanks for the suggestions!

No level shifting required. All switching happens between the MCU and RS232 drivers. System is 3.3V....

I looked at the MAX303 (it's got some funky supply requirements, made more for higher V's.)

But looking at the category in Digikey (IC analog SW) gave me some good search criteria and I've found a lot of good options. Nothing yet with

Thanks again,

John

On 1 Dec 2006 06:03:34 -0800, snipped-for-privacy@gmail.com wrote:

The 74HC4052 Has a maximum Icc of 8 microamps with a Vcc of 6V, so even if it was running 8µA with your Vcc of 3.3V, that's a quiescent dissipation of only 26.4 _micro_ watts.

If you can spare the real estate, you can get the current _way_ down by building the thing out of glue logic.

Here's an LTSPICE circuit file showing one way to do it:

Version 4 SHEET 1 1092 1384 WIRE -16 -528 -608 -528 WIRE 304 -512 48 -512 WIRE 352 -512 304 -512 WIRE 464 -464 416 -464 WIRE 352 -448 128 -448 WIRE 464 -432 464 -464 WIRE 464 -320 464 -352 WIRE 352 -304 -80 -304 WIRE 464 -256 416 -256 WIRE 304 -240 304 -512 WIRE 352 -240 304 -240 WIRE 464 -224 464 -256 WIRE 464 -112 464 -144 WIRE 208 -48 -432 -48 WIRE 304 0 272 0 WIRE -80 16 -80 -304 WIRE 208 16 -80 16 WIRE 304 32 304 0 WIRE 352 32 304 32 WIRE 464 80 416 80 WIRE -80 96 -80 16 WIRE -16 96 -80 96 WIRE 352 96 304 96 WIRE 128 112 128 -448 WIRE 128 112 48 112 WIRE 208 112 128 112 WIRE 464 112 464 80 WIRE 304 128 304 96 WIRE 304 128 272 128 WIRE 208 176 -256 176 WIRE 464 224 464 192 WIRE -608 240 -608 -528 WIRE -432 240 -432 -48 WIRE -256 240 -256 176 WIRE -80 240 -80 96 WIRE -608 400 -608 320 WIRE -432 400 -432 320 WIRE -432 400 -608 400 WIRE -256 400 -256 320 WIRE -256 400 -432 400 WIRE -80 400 -80 320 WIRE -80 400 -256 400 WIRE -608 448 -608 400 FLAG -608 448 0 FLAG 464 -320 0 FLAG 464 -112 0 FLAG 464 224 0 SYMBOL Digital\\\\or 16 32 R0 WINDOW 0 4 15 Left 0 SYMATTR InstName A3 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL voltage -80 224 R0 WINDOW 3 24 104 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 2 4) SYMATTR InstName V1 SYMBOL Digital\\\\or 384 -544 R0 WINDOW 0 -1 12 Left 0 SYMATTR InstName A5 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL Digital\\\\or 384 -336 R0 WINDOW 0 -4 114 Left 0 SYMATTR InstName A6 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL Digital\\\\or 16 -592 R0 WINDOW 0 6 107 Left 0 SYMATTR InstName A8 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL res 448 -448 R0 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL voltage -608 224 R0 WINDOW 3 24 44 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 .1 .2) SYMATTR InstName V3 SYMBOL res 448 -240 R0 SYMATTR InstName R4 SYMATTR Value 10k SYMBOL Digital\\\\and 240 -80 R0 SYMATTR InstName A2 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL Digital\\\\and 240 208 M180 SYMATTR InstName A4 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL Digital\\\\and 384 0 R0 SYMATTR InstName A7 SYMATTR SpiceLine trise 1e-6 tfall 1e-6 vhigh 5V SYMBOL voltage -256 224 R0 WINDOW 3 24 44 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 .2 .4) SYMATTR InstName V4 SYMBOL res 448 96 R0 SYMATTR InstName R1 SYMATTR Value 10k SYMBOL voltage -432 224 R0 WINDOW 3 24 44 Invisible 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 0 1e-6 1e-6 .1 .2) SYMATTR InstName V2 TEXT -408 424 Left 0 !.tran 10 TEXT 72 -552 Left 0 ;TXDATA TEXT -144 328 Left 0 ;A/B- TEXT 480 -456 Left 0 ;TXOUT A TEXT 480 -248 Left 0 ;TXOUT B TEXT 480 88 Left 0 ;RXIN TEXT -704 328 Left 0 ;TXOUT TEXT -536 328 Left 0 ;RXOUTA TEXT -360 328 Left 0 ;RXOUTB

I like it. Do you know of a source? They list Digikey as having them in stock, but Digikey doesn't show them.

If you use them, where do you get them?

Thanks,

John

--- I've not used them yet.

Probably the best way to find a source is to call ON semi.

Also, if you go to their site and search for "analog switch" you'll find a bunch more parts which might work for you. They even have the dual SPDT switch you said you were looking for.

You might also want to try TI, National, and Siliconix. They all make dual SPDT switches.

-- JF