Heres some bits and pieces that might be of interest. INT 14 - SERIAL IO - INITIALIZE USAR

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================= PROGRAMMING THE SERIAL PORT ================== Here's some bits and pieces that might be of interest. ---------------------------------------------------------------- INT 14 - SERIAL I/O - INITIALIZE USART REG AH = 0 REG AL = INITIALIZING PARAMETERS BIT 7 - 6 - 5 4 - 3 2 1 - 0 -BAUD RATE- PARITY STOP WORD BITS LENGTH 000 110 BD 00 NONE 0-1 10 - 7 001 150 BD 01 ODD 1-2 11 - 8 010 300 BD 11 EVEN 011 600 BD 100 1200 BD 101 2400 BD 110 4800 BD 111 9600 BD (4800 ON PCjr) DX = PORT NUMBER ---------------------------------------------------------------- INT 14 - SERIAL I/O - TRANSMIT CHARACTER REG AH = 1 AL = CHARACTER DX = PORT NUMBER ON RETURN: REG AH = RS-232 STATUS CODE BIT 0 = DATA READY 1 = OVERRUN ERROR 2 = PARITY ERROR 3 = FRAMING ERROR 4 = BREAK DETECTED 5 = TRANSMISSION BUFFER REG. EMPTY 6 = TRANSMISSION SHIFT REG. EMPTY 7 = TIME OUT AL = MODEM STATUS BIT 0 = DELTA CLEAR-TO-SEND 1 = DELTA DATA-SET-READY 2 = TRAILING EDGE RING DETECTED 3 = CHANGE, RECEIVE LINE SIGNAL DETECTED 4 = CLEAR-TO-SEND 5 = DATA-SET-READY 6 = RING DETECTED 7 = RECEIVE LINE SIGNAL DETECTED ---------------------------------------------------------------- INT 14 - SERIAL I/O - RECEIVE CHARACTER REG AH = 2 ON RETURN: REG AL = CHARACTER RECEIVED REG AH = RS-232 STATUS CODE (SEE ABOVE) ---------------------------------------------------------------- INT 14 - SERIAL I/O - GET USART STATUS REG AH = 3 ON RETURN: REG AH = RS-232 STATUS CODE (SEE ABOVE) REG AL = MODEM STATUS CODE (SEE ABOVE) ---------------------------------------------------------------- The following applies to COM1 (COM2 addresses are different). ---------------------------------------------------------------- procedure SendChar(C: byte); begin while (Port[$3FD] and $20)=0 do ; Port[$3F8] := C; end; Function ReadChar: byte; begin while not odd(Port[$3FD]) do ; ReadChar:= Port[$3F8]; end; procedure SetSerial(BaudRate: Integer); { Set serial parameters on to COM1:BaudRate,N,8,1 } var x : integer; begin x := trunc(115200.0 / BaudRate); Port[$3FB] := 128; Port[$3F8] := x and 255; Port[$3F9] := x shr 8; Port[$3FB] := 3; {Line Control Register} Port[$3FC] := 3; {Modem Control Register} Port[$3F9] := 0; {Interupt Enable Register} end; ---------------------------------------------------------------- Port(hex) Description 3F8 I/O Transmitter Holding Register / Receiver Data Register 3F8/3F9 O Baud Rate Divisor 3F9 I/O Interupt Enable Register 3FA I Interupt Identification Register 3FB I/O Line Control Register 3FC O Modem Control Register 3FD I Line Status Register (see "RS-232 STATUS CODE" above) 3FE I Modem Status Register (see above for bits) Programming the 8250 Serial Chip. 1. Set Baud Rate. x := trunc(115200.0 / BaudRate); Port[$3FB] := 128; Port[$3F8] := x and 255; Port[$3F9] := x shr 8; Take For example 2400 baud; the following would be needed in Assembly Language: mov dx,3FBh mov al,128 out dx,al mov dx,3F8h mov al,30H out dx,al inc dx mov al,0 out dx,al - You might like to set up a table if more that one baud rate is used. 2. Set LCR ($3FB) Bit 7 Normally 0, set to 1 to change baud rate 6 Normally 0 (Break Disabled). 5 Normally 0, "Stick Parity" disabled 4 Parity: 0 = Odd, 1 = Even 3 Parity: 0 = No parity generated, 1 = Generate parity 2 Stop Bits: 0 = 1 bit, 1 = 2 bits (or 1.5 if Char len = 5 bits) 1+0 Character Length: 00 = 5 bits, 01 = 6 bits, 10 = 7 bits, 11 = 8 bits. For 8 Data Bits, No Parity, 1 Stop Bit - value of LCR is 3 3. Set MCR ($3FC) Bit 7..5 Always 0 4 Loop Back (output goes straight to input) 3 Normally 0, set to 1 for serial interrupt. 2 Not Used 1 Activate RTS line 0 Activate DTR line Value of MCR is normally 3. I won't go into the details of interrupts send me a message if you do need the info. 4. Set up IER ($3F9) This is normally 0. That's all that's needed to set it up. To receive a character: A character is ready in the Receiver Data Register when bit 0 ("Received Data Ready") of line status register is 1. See ReadChar function. To send a character. You must wait until the previous character has been sent. Bit 5 ("Transmitter Holding Register Empty") will be zero when it is O.K for you to send a character. See the SendChar procedure. ==== PY ====

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