/* ****************SCI1.C********
  Jonathan W. Valvano   April 17, 2000
  RS485 half-duplex multiport network  
  Hardware: 
     Adapt812 MC68HC812A4 SCI1 serial port
     RS-485 half-duplex network to other Adapt812s
     6812 PS3/TXD1 connected to SP483 DI data in 
     6812 PS2/RXD1 connected to SP483 RO receive out
     6812 PE6      connected to SP483 DE 1 enables transmission 
     6812 PE5      connected to SP483 RE 0 enables receiver 
     SP483 A-A, B-B, ground-ground */
     
// bits in the SC1SR1 status register
#define TBE 0x80 
#define TC  0x40
#define RDF 0x20

void cycwait(unsigned int cycles){
    TC5=TCNT+cycles;  // number of 125ns cycles to wait
    TFLG1 = 0x20;     // clear C5F
    while((TFLG1&0x20)==0){};}

//-------------------------Start of InitSCI1------------------------
// Initialize Serial port SCI1
void SCI1Init(void){
    SC1BDH=0;      // 9600 BR=52 (MCLK=8MHz) clock 
    SC1BDL=52;     // BR=MCLK/(16*BaudRate)
    TSCR |=0x80;   // TEN(enable)
    TIOS |= 0x20;  // enable OC5
	SC1CR1=0x12;
/* bit value SC1CR1 meaning
    7   0    LOOPS, no looping, normal
    6   0    WOMS, normal high/low outputs
    5   0    RSRC, not appliable with LOOPS=0
    4   1    M, 1 start, 9 bit (8data+parity), 1 stop
    3   0    WAKE, wake by idle (not applicable)
    2   0    ILT, short idle time (not applicable)
    1   1    PE, parity
    0   0    PT, even parity type */ 
    SC1CR2=0x0C; 
/* bit value SC1CR2 meaning
    7   0    TIE, no transmit interrupts on TDRE
    6   0    TCIE, no transmit interrupts on TC
    5   0    RIE, no receive interrupts on RDRF
    4   0    ILIE, no interrupts on idle
    3   1    TE, enable transmitter
    2   1    RE, enable receiver
    1   0    RWU, no receiver wakeup
    0   0    SBK, no send break */ 
    DDRE = 0x60;         // PE6,PE5 control RS485 chip
// PE5=RE=0 enables RS485 receiver
// PE6=TE=1 enables RS-485 transmitter
    PORTE=0x40;     // TE=1, RE=0, enable RS485 transmitter
}
    
//-------------------------Start of SCI1InStatus--------------------------
// Checks if new input is ready, TRUE if new input is ready
// Returns TRUE if a call to SCI1In will return right away
int SCI1InStatus(void)	
{	return(SC1SR1 & RDF);}

//-------------------------Start of SCI1In------------------------
// Wait for new serial port input, return ASCII code for key typed
char SCI1In(int *errPt){ // gadfly wait
// returns by value the ASCII character from the RS485 network
// returns by reference, 1-15 for errors, 0 for no error
	while ((SC1SR1 & RDF) == 0);
	(*errPt)=SC1SR1 & 0x0F;  // Bit3=OR, Bit2=NF, Bit1=FE, Bit0=PF 
	return(SC1DRL);}
	
//-------------------------Start of SCI1Out------------------------
// output ASCII to RS485 channel, wait for echo, check for collision
// receiver always enabled, transmitter always enabled
int SCI1Out(char dataOut){ char echoIn,status; int error;
// returns OK(0), COLLISION(1), TIMEOUT(2) or PARITYERROR(4) 
    error=OK;          // assume no errors
	SC1DRL = dataOut;  // start transmission
  	cycwait(10000);    // 1.25msec (12 bit times)
	status=SC1SR1;
	if(status& RDF){   // should be ready, if not return as a timeout
	  echoIn=SC1DRL;   // capture echo, clear flags
	  if (status & PF) 
		 error|=PARITYERROR;
	  if(echoIn!=dataOut)  // half-duplex, so outgoing should match incoming
	     error|=COLLISION; // collision error, did not match
	}
	else
	   error=TIMEOUT;  // no response 1.25ms after sent
	return error;}

//-------------------------Start of SCI1OutString------------------------
// Output String (NULL termination)
int SCI1OutString(char *pt){ char letter; int error;
    error=0;
    while (letter=*pt++)
       error|=SCI1Out(letter);
	return error;}