Using a 74HC4052 to switch between serial devices

[Ed Arnold]

This is a little off topic, sorry. I have a project which needs 4 serial ports to be polled off of one hardware serial port. I don't wish to use RS422/485. My question is, has anyone tried to use or knows if a 74HC4052 will work? This is a Dual 4 channel analog switch or Mux/Demux. This device can handle +/- 6 volts. So if I attactch it to the TTL side of a MAX232 chip. That should work. My concern is switch times, etc. So, can an analog switch handle a digital signal? At what baud rate will it fail to work? I have scanned over two data sheets, but some of those charts and graphs give me a head ache.

Thanks in advance,

Ed

[Humberto]

Why are you looking for an analog selector if you are dealing with TTL levels?
Try the 74LS352 Dual 4 Line to 1 Line Data Selector.
It�s propagation delays time is in the nanoseconds range.

Keep well,

Humberto

[dyeatman]

I have used the MAX398 in several designs with no problems. Although I have never needed that kind of switching speed, it also appears to have times in the nanosecond range.

[Ttelmah]

The reason is fairly obvious if you think about it. To multiplex both the transmit and receive, requires one device for each data direction, using normal logic chips, but both can be done with a single analog multiplexor.
The 4052, should be fine with any normal data rate. The old Cmos 4066 multiplexer, was commonly used to handle placing text into a video picture, at dot clock rates in the order of 14Mhz. There was some degradation, but not too bad.
The reason for the lack of propogation data, is that unlike a logic gate where there is an internal propogation delay through the device, these multiplexers are effectively FET based bilateral switches, and the delay characteristic is dependant on the FET resistance, the capacitance of the load, and the drive ability of the source. You can model them as a resistor with the same on resistance quoted for the gate, and a capacitor across the output. The propogation data normally quoted, is the time to select a different channel, rather than for data transfers using one of the switches. The typical transfer time through the switch, is fast, only in the order of 4nSec, but the time to select a different channel, is in the order of 300nSec. The output capacitance is normally quoted as 12pF, with the on-state resistance varying according to supply voltage, but in the order of 200R. The typical performance bandwidth is in excess of 20MHz, so should be fine for any serial data rate.

Best Wishes

[Humberto]

[Ed Arnold]

Thank you all for your replies. I got the answers I needed and your info clearified many confusions from the data sheets. I will also look into the 74HC352 that was mentioned.

Thanks Again

Ed

[Ed Arnold]

I was unable to find a data sheet for this part. TI's web site states this part is no longer in production. Digikey, Mouser, etc do not sell them. The only hits I got on Google were the japan surplus dealers. So, if the chip is out of production or near EOL, then putting it in a new product doesn't make sense.

Thanks for the input just the same,

Ed

[Humberto]

[Humberto]

Sorry for posted again. I tested the previous link and didn�t function.
http://www.ortodoxism.ro/datasheets/nationalsemiconductor/DS006425.PDF