petit jc wrote:
>
> I would like to connect a pic (13c84) to the serial port.
> The problem is that I don't want to use any battery and no converter
> 0/5v +12v/-12v.
> I would like to use the line TX at the level (-12 v) and so I need to
> put a regulator between TX and GND. But what about the other lines? How
> can I obtain the correct protocol? It seems that a mouse works like that
> (TX/GND -12v) but I can't find any schematic of a mouse...
> Thanks for response.
> petitj@esiee-amiens.fr


Hi Jc, I don't know why you want to use the TX insted of RTS.
well, this is a circuit that connect to PC via serial port, use no other
power supply than the RS-232 and works up to 19200bps. The PIC can receive
and transmit data.
If you need code, I can send to you, just ask me.

Octavio
nogueira@mandic.com.br


           list n=78, p=PIC16C84, r=HEX
;***************************************************************************
           TITLE "RS232C Interface"
;
;    Comments: PIC-16C84/PC RS232 Interface
;          By: Terry Rudersdorfer, AScT
;        Date: Aug/94
;     Revised: Sep/94 eliminate transistor, diode and resistor on RX
;     Revised: Oct/94 added test led for do something test
;
;       Fuses: XT or HS and PWRTE enabled
;
; This design provides;
;     - full duplex 2400 Baud with 8 bits no parity 1 stop using
;       a standard 5.066 MHz communication xtal.
;     - only 3 resistors to provide an RS232 Tx/Rx electrical interface
;     - power is obtained from the standard RS232 control leads.
;       (RS232 O/P's can sink/source 10mA; this circuit uses < 5mA.)
;
; Simple RS232C - PC to PIC Interface     Aug/94      T. Rudersdorfer, AScT
;  revised Sep/94
;
;   1 - 470 ohm   short circuit current limit
;   1 - 10k       open collecter pull down
;   1 - 47k       power up pull up
;   1 - 470k      injection current limit
;   2 - 15pf      oscillator stabilization
;   1 - .1uf      decouple PIC and regulator
;   1 - 10uf      voltage stabilization
;   1 - 5.0688MHz standard communication xtal
;   1 - 1N4150    reverse voltage blocking diode
;   1 - 78L05     5V low power regulator (100mA Max)
;   1 - 16C84     PIC
;   1 - LED       do something test led
;   1 - 2k7       do something current limit for test led
;
; PC  DTE  DCE
;
;  RX<(3)--(3)-/\/\/\/-----------------------------+--/\/\/\/----+
;                470                               |    10k      |
;                       |\ |                       |            ///
;        +-----/\/\/\/--| >|---------------------+ |
;        |       2k7    |/ |   ---------------   | |
;        |              LED   | 1     U   RA1 |--+ |
;        |   ^ +5V            |           RA0 |----+
;        |   |                | ____  1  Osc1 |------------------+
;        +---+-/\/\/\/--------| MCLR  6  Osc2 |------+           |
;                47k    +-----| Vss   C   Vdd |--+   |     _     |
;                       |  +--| RB0   8       |  |   +---||_||---+
;                      /// |  |       4       |  |   | 5.0688MHz |
;  TX>(2)--(2)-/\/\/\/-----+  |               |  |  _|_         _|_
;               470k          |_______________|  |  ___15pf     ___15pf
;                                                |   |           |
;                  1N4150        _____    ^ +5V  |  ///         ///
;                   |\ |        |     |   |      |
; RTS>(4)--(4)-+----| >|----+---|78L05|---+------+
;              |    |/ |    |  1|_____|3  |
; CTS<(5)--(5)-+           _|_     |2    _|_
;              |           ___10uf |     ___.1uf
; DSR<(6)--(6)-+            |      |      |
;                          ///    ///    ///
; GND (7)--(7)-+
;              |
;             ///
;
; RS232 RX circuit background:
;    Based on AN521 in the 1993 Embedded Handbook; PIC I/O pins can handle
;    +/- 500uA of continuous injected current. This means voltages greater
;    than VDD and VSS CAN BE used as long as adequate current limiting is
;    provided. My original RX input design isolated the PIC by using an
;    extra transistor, diode and resistor. This can be eliminated by using
;    a large enough resistor value in series to the PIC I/O Pin. RS232
;    voltage levels can be up to +/- 15V, therefore, a 470k resistor provides
;    an adequate current limit of 32uA (the same current used in AN521).
;
; RS232 TX circuit background:
;    Researching specification sheets for RS232 receivers like the 1489,
;    reveals that they do not require bipolar voltages to operate. The
;    1489 in fact clips all -ve signals to ground, therefore only requiring
;    +ve and ground input levels.
;
;