Is there any way to make the FT232R RXD and TXD pins as tristate pins, whenever in runtime there ia a need of this?
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There probably is. You can alter the internal workings.
However, I would simply add a tri-state logic buffer. You should only need this on the Tx pin since the Rx is a CMOS logic input.
I need to do something like this on my current project, where the serial data has to come from a "real" RS232 (ie, MAX232) or from the FT232R. I was going to use a simple analog switch (ie 4053) or an And/OR/Invert logic block (not sure of the logic number). One could also use a digital 2:1 mux.
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Im in the midst of laying out a board that shares a USART between USB and RS485. Obviously tri-stating of the Tx/Rx lines is necesary for this.
Im using the FT232BL for this as its UART lines are all tri-stated (but with weak pull-ups) when the chip is in reset. The datasheet recommends using the USB+5V line to drive the FT232BL's reset line (when self-powered) such that it is held in reset whenever the USB is unconnected. When this is the case I can use the AVR's USART thru the RS485 driver.
Also, by connecting an I/O to the FT's reset line, I can monitor when the USB is connected and/or assert the reset to allow RS485 even when USB is connected.
For RS232 versions, I use MAX3221 or MAX3222. These have enable and shutdown pins which you may find useful, Jim.
In my app, both ports access the same function and only one will be in use at a time. So, I don't care if the UART talks to both ports. I do have to merge the receive lines and the FT232 reset line trick might be very useful for that. Thanks
I usually follow Jim's suggestion and have a mux to select the rx signals. The BL device is obsoleted I believe - I'm currently using the RL version.
On the RL device, I think you can use the LDO output of the FT232 to control path switching logic. That ought to work. Have not tried it yet.
A quick check of the FTDI site reveals nothing about the FT232BL being obsolete. Though admittidly it doesnt look like the latest and greatest. You had me a little conserned there for a moment Kartman.
Or the PWREN# or SLEEP# logic outputs (CBUS3 and CBUS4). I've done something similar using PWREN#.
Good point. I had overlooked those pins.
Sorry to scare you Steve, but I haven't touched a B series device for some time. The R series offer many advantages such as no crystal and built in eeprom - a few less parts to worry about.
Wow. The R series looks great. Thanks for the enlightenment Kartman. Also note Jim, that the UART lines go tri-state under Reset the same I described for the B series. (bottom of p.20 of DS) No need for separate buffers. Yay!
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