Listing and additional info for DI #2277:


The default 80186 Timer Register Address are as follows:

Register Name               Timer0      Timer1      Timer2

Mode/Control Word           FF56H       FF5EH       FF66H
Max Count B                 FF54H       FF5CH       NOT PRESENT
Max Count A                 FF52H       FF5AH       FF62H
Count Register              FF50H       FF58H       FF60H

The timer control word bits are as follows:             

Bit 0   Set to 1 for Continous mode running/0 for one shot mode
Bit 1   1 for Timer to alternate between Max Count reg A & B, 0 for A only
Bit 2   1 to select External Clock for the timer, 0 for Internal i.e. CPU 
clock/4
Bit 3   If 1, Timer2 output is used as clock, else internal clock(CPU Clock/4) 
is used
Bit 4   if 0 the Input level gates the timer on or off (timer will count for a 
Hi)
Bit 5   This is a read only bit set when the timer reaches its maximum value
Bit 11  This bit has to be 0
Bit 12  This read only bit Indicates which Max count Reg is in Use(0 indicates 
A)
Bit 13  If set, interrupts will be generated on every terminal count
Bit 14  If 0, Bit 15(Enable/Disable) is ignored, else Bit 15 will take effect
Bit 15  If set, the timer is enabled, 0 will stop the timer

Note: All bits except bit 5 and 12 are read/write. Bit 5 & 12 are read only. 
Bits not shown above are don't care

*/

/* 
For compiling and linking; the following make batch file is used.
libs file contains names of library files which are to be linked.
Note that all addresses are system specific.

ic86 %1.c
link86 %1.obj,&<libs
loc86  %1.lnk ss(stack(+4096)) ad(cs(code(01030h),data(05040h))) ST(main)
*/

#pragma ram
#pragma fp
#pragma la
#pragma mod186
#pragma extend

typedef unsigned char byte;
typedef unsigned int word;

/* IC86 Specific header file */
#include        <icc\i86.h>

void    delay(word count)
{
        word    i;
        for (i=0;i <count;i++);
}

/* System specific addresses and utility routines for serial IO */
#include        <include\addr.h>
#include        <include\SccAsync.c>

/* Starts and stops the counter with Max Reg A in use 
   so that timer1_out is High */
void    MakeHi()
{
        outword(0xff5e,0x4004); /* Stop timer 1 */
        outword(0xff58,0x0);    /* Count  = 0 */
        outword(0xff5a,0xffff); /* Large Max Count A */
        outword(0xff5e,0xc000); /* Start Counter, with int clk, A only, No cont 
0xc004 
*/
        outword(0xff5e,0x4004); /* Stop Timer */
}

/* Starts the timer with Max Reg A and B alternating, Max Reg A is
   set for only 1 count and B for a large count. The timer is stopped as
   soon as Max Reg B is in use so that timer1_out is Lo */
void    MakeLo()
{
        outword(0xff5e,0x4003); /* Stop Timer1 */
        if ((inword(0xff5e) & 0x1000) != 0x1000) 
        /* If output is now high; ie. A is in use, Make output Lo */
        /* Else output already Low; do nothing */
        {
                outword(0xff58,0x0); /* Count  = 0 */
                outword(0xff5a,0x1); /* Max Count A = 1 */
                outword(0xff5c,0xffff);/* Max Count B = Large value */
                /* Start Counter, with int clk, Max Reg A&B, not continuous mode */
                outword(0xff5e,0xc002); 
                /* Wait till B in use ie. Output goes Low */
                while ((inword(0xff5e) & 0x1000) != 0x1000);
                outword(0xff5e,0x4002); /* Stop Timer */
        }
}

/* Timer0 is kept running with RTG bit = 0 so that the timer is turned
   on or off depending on whether the Timer0_in is Hi or Lo. This routine
   tests the state of Timer0_in pin by checking if the timer is incrementing */
byte    ReadInput(void)
{
        outword(0xff50,0); /* reset count register */
        delay(3);
        if (inword(0xff50) > 0) /* if counting */
                return(1); /* Timer0_in is High */
        else return(0);
}       
        
main()
{
        byte    string[300];
        byte    chr;

        init_stack();   /* Assembly routine for initialising stack pointer SP 
and base 
SS .*/
        outword(0xff56,0xc001); /* Start timer0 in continuous mode,RTG=0 */
        while (1)
        {
                PrintString("Enter Level to be Output(1/0):");
                chr = GetChar();
                if(chr == '1') 
                {
                        PrintChar('1');
                        MakeHi(); /* Output Level 1 */
                }
                else 
                {
                        PrintChar('0');
                        MakeLo(); /* Output Level 0 */
                }
                PrintChar(' ');
                PrintString("Input Level is  = ");
                if(ReadInput()) 
                        PrintChar('1');
                else PrintChar('0');
                crlf();
        }
}