Post by thread:Request for info on PIC <--> RS232 interfacing.

RS232 interfacing made easy. What you need: -------------- 1. MAX232 / MAX233 Why you need: ------------- 1. VOLTAGE LEVEL CONVERSION ------------------------- The MAX232/3 acts as a voltage level converter. It converts the 0/5V TTL level of the PIC to +12/-12V level of the RS232 target system. The MAX232 employs a charge pump to achieve the larger voltage. The charge pump requires external resistors / capacitors for the MAX232. The MAX233 has these resistors / capacitors on chip & therefore offers a SINGLE CHIP TTL <--> RS232 VOLTAGE LEVEL CONVERTER. What you need to know: ---------------------- The MAX232/3 contains two receive & two transmit buffers (ie you can convert two different TTL signals to RS232 & two different RS232 signals to TTL). For a bare-bones-up-and-running-quickly implementation you need only one transmit and one receive buffer. For handshaking (if it's necessary) the spare transmit and receive buffer can be used for CLEAR_TO_SEND (CTS) and REQUEST_TO_SEND (RTS) signals. Using these spare buffers in this way will improve communication reliability. Example (My first attempt at ascii art!) : -------- BARE-BONES-UP-AND-RUNNNG-QUICKLY IMPLEMENTATION: [RS232:+12/-12V] [TTL:0/5V] MAX232/3 PIC ___ ___ | +5V | +5V --------- ------- | | RB0 | | TARGET TX | |\ | PIC RX | | ________\___|___| \___|__\______________| |_____ / | | / | / | | | | |/ | | | ---- | | RB1 | | |||| TARGET RX | /| | PIC TX | | ---- ________/___|___/ |___|__/______________| |_____| \ | \ | | \ | | crystal | \| | | | | | | | --------- ------- | | | Ground ---- ---- \ / \ / \/ \/ TARGET GROUND PIC GROUND _______________________________________ | | | | ---- ---- \ / \ / \/ \/ The PIC exteranal interrupt pin may be used to signal the receipt of a START bit. The remaining bits are then received in software from this pin. Where to find out more: ----------------------- 1. PIC AN510 application note: "implementation of an asynchronous Serial I/O" at various PIC ftp sites. 2. Serial communications FAQs: http://www.paranoia.com/~filipg/HTML/LINK/PORTS/F_Parallel.html Take Care, Chris Madden

> RS232 interfacing made easy. > > What you need: > -------------- > 1. MAX232 / MAX233 Anyone know of a solution like this that allows you to tri-state the RS232 outputs? (The +/-12V side - NOT the TTL side.) -- -- Paul Greenwood -- (spam_OUTpabloTakeThisOuTaustin.ibm.com) For an idea to be fashionable is ominous, since it must afterwards be always old-fashioned. "His super power is to turn into a scotch terrier."

Some of the Linear Technology RS232 transcievers let you externally shut down the chip, I don't recall if it puts the inputs and outputs in a high-Z state. On Fri, 19 May 1995, Paul Greenwood wrote: {Quote hidden}> > RS232 interfacing made easy. > > > > What you need: > > -------------- > > 1. MAX232 / MAX233 > > Anyone know of a solution like this that allows you to tri-state the RS232 > outputs? (The +/-12V side - NOT the TTL side.) > > -- > -- Paul Greenwood -- (.....pabloKILLspam@spam@austin.ibm.com) > For an idea to be fashionable is ominous, since it must afterwards be > always old-fashioned. > > "His super power is to turn into a scotch terrier." >

>> RS232 interfacing made easy. >> >> What you need: >> -------------- >> 1. MAX232 / MAX233 > >Anyone know of a solution like this that allows you to tri-state the RS232 >outputs? (The +/-12V side - NOT the TTL side.) > >-- > -- Paul Greenwood -- (pabloKILLspamaustin.ibm.com) >For an idea to be fashionable is ominous, since it must afterwards be >always old-fashioned. > >"His super power is to turn into a scotch terrier." I'm no expert but I might try using a diode to turn the RS232 Level to pullup only and use a terminating resistor to pull the line low at the end of your chain of devices. Doug Sellner Beach Tech 4131 Vincent Avenue South Minneapolis MN 55410 Voice (612) 924-9193 x 521 Fax (612) 926-1145 Internet: .....dsellnerKILLspam.....embay.com