Post by thread:Putting RS232 TX line high

At 14:14 3/10/98 -0500, you wrote: >Does anyone know off-hand the memory address and value for setting the RS232 >TX line high on a PC? I need to trigger a relay connected to this line. > >Thanks. > >C. Webb Hi, First of all, what do you mean HIGH on TX line on RS232 port of PC ? The TX and RX lines (in RS232) are not on TTL level. The 'logic 1' on TX (idle state) means this line is about -12V respect to ground, the 'logic 0' on TX (mark state) means this line is about +12V respect to ground. Apart from this, you can't change the state of TX in this way (to control relay). Instead of TX, use the RTS or DTR signal. These signals are TTLs, and it is easy to use as general purpose bits. To change these signals, set or clear the appropriate bit: (DTR) [baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8, so the appropriate bit is the lsb of 0x3fc) (RTS) [baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8, so the appropriate bit is the second bit of 0x3fc) bye csaba

Craig Webb wrote: >At 14:14 3/10/98 -0500, you wrote: >>Does anyone know off-hand the memory address and value for setting the RS232 >>TX line high on a PC? I need to trigger a relay connected to this line. >> >>Thanks. >> >>C. Webb The Csaba replied with: {Quote hidden}>Hi, >First of all, what do you mean HIGH on TX line on RS232 port of PC ? >The TX and RX lines (in RS232) are not on TTL level. >The 'logic 1' on TX (idle state) means this line is about -12V respect >to ground, the 'logic 0' on TX (mark state) means this line is about +12V >respect to ground. >Apart from this, you can't change the state of TX in this way (to control >relay). >Instead of TX, use the RTS or DTR signal. >These signals are TTLs, and it is easy to use as general purpose bits. >To change these signals, set or clear the appropriate bit: >(DTR) >[baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8, >so the appropriate bit is the lsb of 0x3fc) >(RTS) >[baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8, >so the appropriate bit is the second bit of 0x3fc) RTS or DTR are NOT TTL level signals. You will have to pass them through a level translator (such as a 1489 or the RX half of a MAX232) to get TTL/CMOS level outputs. From here, the signals can be used to control a relay driver (such as a ULN2003A). myke "If people don't know what you're doing, they don't know what you're doing wrong." - Sir Humphrey Appleby K.C.B

Craig Webb wrote: > > Does anyone know off-hand the memory address and value for setting the RS232 > TX line high on a PC? I need to trigger a relay connected to this line. > > Thanks. > > C. Webb Probably better to use the DTR or RTS lines for this sort of job, as they are direct digital outputs. Set them HI or LO by writing to the MCR (Modem Control Register) in the PC's UART. MCR bit 0 drives DTR MCR bit 1 drives RTS The address of the MCR is 03FCh, for COM1 where base-address is 03F8h, use same offset if other port at other base address. Hope this is of use jim ford

{Quote hidden}> >Does anyone know off-hand the memory address and value for setting the RS232 > >TX line high on a PC? I need to trigger a relay connected to this line. > > > >Thanks. > > > >C. Webb > > Hi, > First of all, what do you mean HIGH on TX line on RS232 port of PC ? > The TX and RX lines (in RS232) are not on TTL level. > The 'logic 1' on TX (idle state) means this line is about -12V respect > to ground, the 'logic 0' on TX (mark state) means this line is about +12V > respect to ground. > Apart from this, you can't change the state of TX in this way (to control > relay). > Instead of TX, use the RTS or DTR signal. > These signals are TTLs, and it is easy to use as general purpose bits. > To change these signals, set or clear the appropriate bit: > (DTR) > [baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8, > so the appropriate bit is the lsb of 0x3fc) > (RTS) > [baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8, > so the appropriate bit is the second bit of 0x3fc) > > bye > csaba > The baseaddress can be found in the ROM BIOS parameter area at addresses: 0000:0400 COM1 0000:0402 COM2 0000:0404 COM3 0000:0406 COM4 0000:0408 LPT1 0000:040A LPT2 0000:040C LPT3 0000:040E LPT4 The ones that doesn't exist have 0 as baseaddress. -------------------------------- Ruben Jvnsson spam_OUTmaxrubenTakeThisOuTmail.bip.net --------------------------------

Ruben Jvnsson wrote: > > > >Does anyone know off-hand the memory address and value for setting the RS232 {Quote hidden}> > >TX line high on a PC? I need to trigger a relay connected to this line. > The baseaddress can be found in the ROM BIOS parameter area at > addresses: > > 0000:0400 COM1 > 0000:0402 COM2 > 0000:0404 COM3 > 0000:0406 COM4 > 0000:0408 LPT1 > 0000:040A LPT2 > 0000:040C LPT3 > 0000:040E LPT4 > > The ones that doesn't exist have 0 as baseaddress. But beware! Ports that are 'virtualized' under NetWare DOS clients have "NW" as their address value. This is done so that programs that test just for presence of the port by looking for zeros find a port there (and writing to the port by means of the BIOS then will work because the NW client traps that). Because no parallel/serial port is present at that address, you'd better check for 0 as well as "NW" (0x4e57 or was it 0x574e?) there. Frank ------------------------------------------------------------------------ Frank A. Vorstenbosch <UCE_ACCEPT="NONE"> Phone: 0181 - 636 3000 Electronics and Software Engineer Mobile: 0976 - 430 569 Eidos Technologies Ltd., Wimbledon, London Email: .....favKILLspam@spam@eidos.co.uk

Thanks for the feedback everyone. I apologize for not making myself clearer. I don't know the why behind it, but whoever designed the system I'm working with said I have to set the TX bit high. I asked the same question about voltages and inverted signal, etc. at the RS-232 end, but the engineer told me all that has to be done is to hold the PC port bit high (I guess on the UART before the MAX232 or whatever it is). So unfortunately DTR & RTS bits won't help, but thanks for the suggestion. If there is no direct memory mapped address to the TX bit, perhaps I have to send a continual stream of bytes=0FFh? Any ideas? Craig {Quote hidden}>>Does anyone know off-hand the memory address and value for setting the RS232 >>TX line high on a PC? I need to trigger a relay connected to this line. >First of all, what do you mean HIGH on TX line on RS232 port of PC ? >The TX and RX lines (in RS232) are not on TTL level. >The 'logic 1' on TX (idle state) means this line is about -12V respect >to ground, the 'logic 0' on TX (mark state) means this line is about +12V >respect to ground. >Apart from this, you can't change the state of TX in this way (to control >relay). >Instead of TX, use the RTS or DTR signal. >These signals are TTLs, and it is easy to use as general purpose bits. >To change these signals, set or clear the appropriate bit: >(DTR) >[baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8, >so the appropriate bit is the lsb of 0x3fc) >(RTS) >[baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8, >so the appropriate bit is the second bit of 0x3fc)

At 03:39 PM 3/11/98 -0500, you wrote: >Thanks for the feedback everyone. I apologize for not making myself clearer. >I don't know the why behind it, but whoever designed the system I'm working >with said I have to set the TX bit high. I asked the same question about >voltages and inverted signal, etc. at the RS-232 end, but the engineer told >me all that has to be done is to hold the PC port bit high (I guess on the >UART before the MAX232 or whatever it is). So unfortunately DTR & RTS bits >won't help, but thanks for the suggestion. > >If there is no direct memory mapped address to the TX bit, perhaps I have to >send a continual stream of bytes=0FFh? Any ideas? > >Craig Sorry, Craig, but sending continuous 0xFF won't do the trick because either the start bit or the stop bit (I can't remember which) is a low value, to distinguish it from the other one, which is a high value. Sean +--------------------------------+ | Sean Breheny | | Amateur Radio Callsign: KA3YXM | | Electrical Engineering Student | +--------------------------------+ Fight injustice, please look at http://homepages.enterprise.net/toolan/joanandrews/ Personal page: http://www.people.cornell.edu/pages/shb7 shb7KILLspamcornell.edu Phone(USA): (607) 253-0315

Hi Craig, >Thanks for the feedback everyone. I apologize for not making myself clearer. >I don't know the why behind it, but whoever designed the system I'm working >with said I have to set the TX bit high. I asked the same question about >voltages and inverted signal, etc. at the RS-232 end, but the engineer told >me all that has to be done is to hold the PC port bit high (I guess on the >UART before the MAX232 or whatever it is). So unfortunately DTR & RTS bits >won't help, but thanks for the suggestion. > >If there is no direct memory mapped address to the TX bit, perhaps I have to >send a continual stream of bytes=0FFh? Any ideas? Sending a continous stream of 0x0FF will just send a +12V "blip" on the line. If you want to output a continuous +12V from the RS-232 port, set bit 6 of the "Line Control Register" (Base Register + 3), which is the "Set Break" bit. By setting this bit, you will, for all intents and purposes disable the serial port's transmitter and just send a "Space" (or +12V). I *think* this is what the engineer is trying to tell you, but if this doesn't work, maybe he should go back to RS-232 school. myke {Quote hidden}>Craig > >>>Does anyone know off-hand the memory address and value for setting the RS232 >>>TX line high on a PC? I need to trigger a relay connected to this line. > >>First of all, what do you mean HIGH on TX line on RS232 port of PC ? >>The TX and RX lines (in RS232) are not on TTL level. >>The 'logic 1' on TX (idle state) means this line is about -12V respect >>to ground, the 'logic 0' on TX (mark state) means this line is about +12V >>respect to ground. >>Apart from this, you can't change the state of TX in this way (to control >>relay). >>Instead of TX, use the RTS or DTR signal. >>These signals are TTLs, and it is easy to use as general purpose bits. >>To change these signals, set or clear the appropriate bit: >>(DTR) >>[baseaddr+4].0 (ie. base address of serial port, eg. com1=0x3f8, >>so the appropriate bit is the lsb of 0x3fc) >>(RTS) >>[baseaddr+4].1 (ie. base address of serial port, eg. com1=0x3f8, >>so the appropriate bit is the second bit of 0x3fc) > > "If people don't know what you're doing, they don't know what you're doing wrong." - Sir Humphrey Appleby K.C.B

On Wed, 11 Mar 1998 15:39:00 -0500 Craig Webb <.....lucidKILLspam.....MAGNET.CA> writes: >If there is no direct memory mapped address to the TX bit, perhaps I >have to >send a continual stream of bytes=0FFh? Any ideas? There is a "set break" bit which, when set, disables the normal transmitter logic and forces the TX line "high" (positive RS-232 voltage). I don't have the book here but I think it's in the same register that controls the number of bits per character, parity, etc. Maybe 3FB, bit 7 but this is strictly a guess. Sending 00 repeatedly would hold the TX line positive for 10/11 of the time, however the stop bits would still make it negative periodically. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]

> > Does anyone know off-hand the memory address and value for setting the RS232 > TX line high on a PC? I need to trigger a relay connected to this line. > > Thanks. > > C. Webb Craig, As other posters have pointed out, the serial ports on an Intel-PC are built for sending and receiving "formatted" async bitstreams on the TX and RX lines. As far as I know, there's no way of directly bit-banging the TX and RX lines, which is what it sounds like you're trying to do. Why not use the modem control lines (RTS,DTR), as other posters have suggested, and simply re-wire the cable to look at one of _those_ lines? Or, since some cables aren't easy to re-wire, pick up an under-$10 "breakout" box from RadioShack(TechAmerica) and wire it to cross (say) DTR on the Intel PC side to the cable's TX line? Then just plugh teh adapter box into the circuit... There may be reasons why this won't work ("It's an imperfect universe" (;-); even so, if we can learn those reasons, it might help define a better answer to your problem. Hope this helps... Frank McKenney / OS/2 Advisor (OS2BBS) McKenney Associates / Richmond, Virginia / (804) 320-4887 Internet: EraseMErrs0059spam_OUTTakeThisOuTibm.net / TalkLink: WZ01123

Frank A. Vorstenbosch wrote: > But beware! Ports that are 'virtualized' under NetWare DOS clients > have "NW" as their address value. This is done so that programs that > test just for presence of the port by looking for zeros find a port > there (and writing to the port by means of the BIOS then will work > because the NW client traps that). An interesting detail which I will spirit away. Not terribly practical though. Prior to Windoze, no usable BIOS *existed* for the COM ports and therefore all comms programs contained their own COM port drivers, or used generic ones in which case NetWare *may* have provided network-compliant versions of some popular generic drivers. Windoze contains comms drivers, but if you try to access COM ports directly, it gets a bit upset, particularly if it determines a program (and that includes the O/S itself, and notably the mouse driver) is already using that port. In summary, those that *knew* pointed out that you can "bit-bang" the TX Data line quite effectively using the "Set Break" bit, though I wouldn't guarantee accurate timing. Bit-banging the RTS and DTR lines is also very easy and routinely used to implement synchronous protocols, receiving data on the CTS, DTR and CD lines in the same fashion. This can even be done while the TXD is in use for normal, separate serial data (just as LapLink does!). *All* these lines are RS-232 (insofar as the machine provides) at the connector. OTOH, most relays would not respond to the sub-millisecond interruptions of a continuous stream of $FF characters sent at 1200 baud and above anyway. Indeed, capacitive coupling and a rectifier would make a very good "fail-safe" system with such a signal source. Cheers, Paul B.