Contributor: THORSTEN BARTH
{> Can anybody give me any info on how to read signals from pins on say> COM2: or from LPT1: or even from The joystick port? I think it has> been done with the PORT command or something, but what are the values> to use to read them with? Thanks.
You can read in signals from different pins on LPT ports with the PORT
command ( =OUT/IN command in assembler). Just determine the base adress of
the LPT port using
}
LPTadress := MemW[40ドル : 6 + LPTNr * 2];
{
where LPTNr is the number of the LPT port from 1 to 3.
Should return 03BCh, 0378h or 0278h.
That has to be done once at the beginning of the program.
Now you can start to read/write values on this port.
The LPT port has:
- 8 data outputs (pin 2 to 9), which can be written using
}
Port[LPTAdress] := B;
{
where B is a byte consisting of the 8 bits. Voltage will be 5V for 1, and 0V
for 0. (but not very high power available (TTL/CMOS)
- 4 handshake outs which can be written by
}
Port[LPTAdress + 2] := B;
{
where B is a byte with the lowest 4 bits set to the values of the pins and
the higher 4 bits always set to zero.
PIN 1: Strobe --> bit 0
PIN 14: AutoFD --> bit 1
PIN 16: Init --> bit 2
PIN 17: SelIN --> bit 3
Attention! bit 2/pin 16 is 0V when set to zero, all others
are INVERTED! (0 --> 5V and vice versa)
- 5 handshake inputs which can be read by
}
B := Port[LPTAdress + 1];
{
After the command, B contains the signals that are connected to the
input pins of the LPT port:
Bit 0-2: no function
Bit 3 --> PIN 15/Error
Bit 4 --> PIN 13/Select
Bit 5 --> PIN 12/PaperEmpty
Bit 6 --> PIN 10/Acknowledge
Bit 7 --> PIN 11/Busy ===> Attention! This input is INVERSE!
For information: The pins 18 to 25 are Signal Ground pins.
To use the inputs, connect TTL level 0V for 0, and 5V for 1 to them.
(Or just use a resistor 10kOhm against +5V (take it from the keyboard
connector or so, don't know what pin that is :-( and a switch against GND:
then you can read in the status of the swith: CLOSED: 0, OPEN: 1...)
}