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LPT1 25 pin port.How can the Tx pin2 and RX pin3 be used 1
- Thread starter kwoody
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The LPT can not be used as a serial device as such. RS232 voltages are swung between -12v and +12 v and the LPT is a 0v to 5v swing. And the LPT can get damaged with the -12, and possibly with the +12 but less certain.
There are ways to emulate the voltage swings with parallel ports. But the voltages will be from 0 to +5 (if you are lucky).
You probably can find out about it by doing a google search "bit banging on the parallel port". But it requires software to be working pretty heavily in doing the timing.
Earlier computers did bit-banging through parallel ports but had voltage conversion chips on the output side to generate the proper voltage swings.
Ed Fair
Give the wrong symptoms, get the wrong solutions.
There are ways to emulate the voltage swings with parallel ports. But the voltages will be from 0 to +5 (if you are lucky).
You probably can find out about it by doing a google search "bit banging on the parallel port". But it requires software to be working pretty heavily in doing the timing.
Earlier computers did bit-banging through parallel ports but had voltage conversion chips on the output side to generate the proper voltage swings.
Ed Fair
Give the wrong symptoms, get the wrong solutions.
- Thread starter
- #4
The concept of bit banging is to provide a parallel-serial conversion. I was looking to use the pin3 once marked 'serial'. I have source of +/- 8V "RS232 data" from a GPS emulator. This was converted to 0-5v using a p-n-p transistor and 2 resistorsbut pin 3 was too heavy a load
Investigation showed that the serial pin(3)in a parallel port when the computer with O/S win98 is on, acts like a 86-100 ohm resistance to gnd, equivalent to a conducting n-p-n transistor sinking 50mA.
Both my Toshiba laptops (1995 and 1999)gave the same effect. In an old book on DOS5 there is a software article on changing a parallel port to a serial port, but nothing about the pin labelled serial.
It seems therefore, that possibly before Win95, pin 3 in the parallel LPT1 might have been used as a serial port
I could find no info.on Google to help. iT may be ;ossible using software to turn off this conducting transistor on pin 3
Kwoody
Investigation showed that the serial pin(3)in a parallel port when the computer with O/S win98 is on, acts like a 86-100 ohm resistance to gnd, equivalent to a conducting n-p-n transistor sinking 50mA.
Both my Toshiba laptops (1995 and 1999)gave the same effect. In an old book on DOS5 there is a software article on changing a parallel port to a serial port, but nothing about the pin labelled serial.
It seems therefore, that possibly before Win95, pin 3 in the parallel LPT1 might have been used as a serial port
I could find no info.on Google to help. iT may be ;ossible using software to turn off this conducting transistor on pin 3
Kwoody
Absolutely NOT. Never was. Pins 2 and 3 are related to the RS232 a thru c specifications and the serial data communications pinouts of the D25 connector as related to the UARTS and line driver/ line receiver chips. (or functional equivalents)
I can't remember the other manufacturer's part numbers, but the Mororola were 6850 (serial) and 6820(parallel). (8250, 16450,16455, and 16550 are some of the NS serials)
Pin 3 on a D25S on a parallel port is not a serial port. It is data2 if I recall. Pin 1 is stobe, 2-9 data, and 10 is ack.
There are hardware chips in the market that have mixed serial/parallel outputs. You select the type of I/O via firmware during POST but using them one way or the other requires hardware glue to make them work.
The port sinks to 0v. That is why it is denoted as /data2. But there is a corresponding input register that can read the voltage on the pin. That is how the bidirectional stuff is read. You throw the output data pin high and you can read what is there, within the limits of under .8 for a zero volt level.
Ed Fair
Give the wrong symptoms, get the wrong solutions.
I can't remember the other manufacturer's part numbers, but the Mororola were 6850 (serial) and 6820(parallel). (8250, 16450,16455, and 16550 are some of the NS serials)
Pin 3 on a D25S on a parallel port is not a serial port. It is data2 if I recall. Pin 1 is stobe, 2-9 data, and 10 is ack.
There are hardware chips in the market that have mixed serial/parallel outputs. You select the type of I/O via firmware during POST but using them one way or the other requires hardware glue to make them work.
The port sinks to 0v. That is why it is denoted as /data2. But there is a corresponding input register that can read the voltage on the pin. That is how the bidirectional stuff is read. You throw the output data pin high and you can read what is there, within the limits of under .8 for a zero volt level.
Ed Fair
Give the wrong symptoms, get the wrong solutions.
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