Post by thread:[PIC]: multiplex UART

On Tue, 23 Oct 2001 09:49:41 -0700, you wrote: >Hi all, > >I need two uarts on a project , which i use 16F877 . Is there any way to multiplex the USART of the pic . Yes, as long as you only need to use one at a time - just use an external mux (74HC157) controlled by a spare pin. -- http://www.piclist.com hint: To leave the PICList .....piclist-unsubscribe-requestKILLspam@spam@mitvma.mit.edu

part 1 1652 bytes content-type:text/plain; (decoded 7bit) Rasit, Someone already mentioned using a multiplexer IC. You can also use OR gates to multiplex the USART TX. See the attached GIF. You select the desired output by applying a LOW to the associated OR gate control line. This arrangement allows you to have both TX outputs OFF, either one ON, or BOTH ON. When the control input to the OR gate is HIGH, the output of the OR gate is forced HIGH, which is the usual MARKING state. I offer this as an alternative to using a multiplexer IC in those cases where you might already have two OR gates available, or where you might want to sometimes enable BOTH TX outputs at once. You may likewise use OR gates to multiplex two UART RX signals in to the single PIC RX line. In this case you need to ensure that the two OR gate outputs do not fight one another. Connect the cathode of a diode to each OR output. Connect the anodes together and to the PIC RX line. Connect a 4.7k pullup from the PIC RX line to +5. You can share control lines to the corresponding TX and RX multiplexers, so that selecting TX A will also select RX A, for example. Fr. Tom McGahee {Original Message removed} part 2 5471 bytes content-type:image/gif; (decode) part 3 105 bytes -- http://www.piclist.com hint: To leave the PICList piclist-unsubscribe-requestKILLspammitvma.mit.edu