Patrick wrote:
> Date: Tue, 24 Sep 1996 08:43:08 +1000
> From: Patrick Hanson
> Subject: Connecting multiple rs232 lines together
>
> I am hoping somebody out there in PIC land may be able to help me.
> I am currently working on a simple home automation system using multiple
> 16C84's (max of 10) fitted with rs232 trancievers as slaves and a PC as
> the master controller. I am not sure how to go about connecting all the TXD
> lines on the slaves to the PC without causing possible conflicts. It is
> intend
Gerard Chew wrote:
>
> What I'm looking for is like, ok, you connect one pin of the
> Stamp to the Tx, one to the Rx and then ...etc? What about some sample code
> to tie the whole thing together?
I sent the following message a few days ago to Mr. Gerard
My 75156 parts just arrived to me but I did not stick them to my prototipe
because I have been busy with overdue projects for my work. However I'll try a
sketch to you (in a robot style!!!?).
Pin 8: to +5 Vdc
Pin 5: to GND
Pins 6/7: to RS-485 link (twisted pair) (field wiring)
Pin 1: Rx Data, to a input port pin of STAMP
Pin 4: Tx Data, to a output port pin of STAMP
Pin 3: TX Enable, to another output port pin of STAMP
Pin 2: Rx Enable, to another output port pin of STAMP
This requires four pins of STAMPs (too much)
A more economical approach should be tie pin 3 and 2 toghether to a output of
STAMP. This signal means: 0 -> STAMP receiving or 1 -> STAMP transminting.
If you want to reduce again the pin counts (in STAMP), tie pins 1 and 4
toghether to a STAMP pin. This STAMP port shall be bi-directional, in another
words, this pin will be output when STAMP is transmiting and will be input when
STAMP is receiving. It's easely implemented with tri-state capabilities of
STAMP.
Two pins looks like:
------ ---------------
|output pin (flow ctrl) 2,3 | |6 RS-485 Link
|---------------------------| |------------ DATA
STAMP | | 75156 |
|in/out pin (data) 1,4 | |7
|---------------------------| |------------ /DATA
| | |
------ ---------------
Sorry I don't write one line of source code yet! But in slave STAMP you must be
in receive mode *listening* to master queries (pins 2,3 -> 0 and pins 1,4 ->
input to STAMP).
I foud National Semi DS75176B at $1 in 500 qty
When I hookup my prototipe I will tell you if it worked out.
I suppose this arrangement work without problems but I'm not sure
Also, I'm interested in a one master many slaves simple protocol. Any pointer?
Luiz