Code:
// ---------------------------------------------------------------------
// S628.c Study/experiment with interrupt driven serial
// communications with a PIC-equiped device as DCE.
//
// Author: Rob Hamerling.
// Date: February 2004.
// E-mail: info@robh.nl
// homepage: http://www.robh.nl
// ---------------------------------------------------------------------
//
// Function: echo incoming datastream from DTE back to DTE
// Features:
// - Interrupt driven, high speed, full duplex data flow (57600 bps)
// - Use of builtin USART in RS232 mode (8 bits, no parity).
// - With relatively large receive buffer.
// - Using CTS flow control (PC -> PIC).
// PC-side should have set CTS output flow control enabled,
// PC FiFo transmit load count may be set to 16 (max).
// - While DTE inactive (RTS false) the PIC slumbers. It gives a 'being
// alive' signal by slowly flashing the RTS light. It is waked-up by
// RB0 (to which RTS is connected)
// - Note: no RTS flow control (PIC -> PC)!
//
// Language support: CC5X compiler version 3.1
//
// Hardware: PIC 16F628 or similar with UART, and MAX232.
//
//
// ---------------------------------------------------------------------
//
// Simplified schematics:
// COMx plug
// PIC16F628 MAX232 RS232 DB9 DB25
// +-------------+ +-----------+
// | | | |
// | RA2 (1)|-----|(11)---(14)|--->-- CTS --- 8 5
// | RB0 (6)|-----|(12)---(13)|---<-- RTS --- 7 4
// | | | |
// | RB1 (7)|-----|(9)-----(8)|---<-- TxD --- 3 2
// | RB2 (8)|-----|(10)----(7)|--->-- RxD --- 2 3
// | | | |
// | (5) | | (15) |
// +------|------+ +----|------+
// +-----------------+----------- GND --- 5 7
//
// +-< DTR --- 4 20
// Optional cable wraps: |
// (maybe required by PC softw.) +-> DSR --- 6 6
// +-> DCD --- 1 8
//
// ---------------------------------------------------------------------
// Some basic PIC and RS232 knowledge will be needed to fully understand
// the data flow and control signalling used in this program.
//
// The PIC ports use positive logic:
// '1' is positive voltage, '0' is ground.
//
// This program uses positive logic for boolean variables:
// the symbol TRUE for '1', the symbol FALSE for '0'.
//
// In the RS232 standard:
// - Negative voltage ('mark') means OFF for control signals, and
// indicates 1 (one) for a data signals (start-, data-, stop-bits).
// - Positive voltage ('space') means ON for control signals and
// 0 (zero) for start-, data- and stop-bits.
//
// Since the MAX232 is not only a level convertor (between TTL and RS232)
// but also a signal inverter, you should be aware of the following:
// - The inversion of PIC data-in and data-out by the MAX232 is required
// to convert data-, start- and stop-bits to/from the corresponding
// RS232 polarity. So nothing special has to be done in the program.
// - For RTS and CTS the inversion by the MAX232 inversion is NOT desired,
// and therefore the program uses inverted signaling for RTS and CTS:
// 'FALSE' is used for ON and 'TRUE' for OFF with RTS/CTS signals!
// As a reminder for this 'inversed' logic the signals are called
// here CTSinv and RTSinv.
//
// -------------------------------------------------------------------------
// For other examples and useful learning material see also:
// - MicroChip datasheets (for the PIC16F62X: DS30400C).
// - Tony Kubek's example for the PIC16F876,
// ASM, interrupt driven, no CTS flow control, single byte buffer.
// - Fr. Thomas MacGhee's example for the PIC16C74,
// ASM, not interrupt driven, but contains many educational notes.
// -------------------------------------------------------------------------
#pragma chip PIC16F628 // target PIC
#include <int16cxx.h> // interrupt support
#pragma config &= ~0b11.1111.1111.1111 // all OFF
#pragma config |= 0b11.1111.0110.0110
// x xx FOSC = HS
// x WDT enabled
// x x BOD enabled (forces /PWRTE)
// x LVP disabled (makes RB4 free)
// xxxxxxx no memory protection
#pragma config ID = 0x6281 // firmware ID (optional)
#pragma bit CTSinv @ PORTA.2 // CTS signal to DTE (PC)
#pragma bit RTSinv @ PORTB.0 // RTS signal from DTE (PC)
#pragma bit RTSled @ PORTB.3 // visual RTS signal
typedef bit BOOL, BOOLEAN; // boolean variable type(s)
#define FALSE 0 // PIC: off, low
#define TRUE 1 // PIC: on, high
#define OSCFREQ 20000000 // oscillator frequency
#define TMR1COUNT (OSCFREQ/4/1000) // 16-bits count for 1 ms
// (prescaler 1:1)
#define BPSRATE 57600 // desired speed
#define BPSCLASS TRUE // BRGH setting (high)
#define BPSCOUNT ((10*OSCFREQ/16/BPSRATE-5)/10) // SPBRG (BRGH=1)
// closest integer value
#define XMTBUFSIZE 32 // output buffer size
#define RCVBUFSIZE 64 // input buffer size
#define DELTA 17 // minimum free rcv buffer ..
// .. space (PC UARTFiFo + 1)
int8 xmtoffset; // offset next byte to xmit
int8 putoffset; // offset last appl. out byte
int8 rcvoffset; // offset next byte to receive
int8 getoffset; // offset last appl. in byte
char xmtbuf[XMTBUFSIZE]; // circular output buffer
bank1 char rcvbuf[RCVBUFSIZE]; // circular input buffer
// located in RAM bank1!
// ----------------------------
// Interrupt service routine
// ----------------------------
#pragma origin 4 // hardware requirement
extern interrupt isr(void) {
char save_FSR; // FSR save byte
char x; // intermediate byte value
int_save_registers // save registers
save_FSR = FSR; // save FSR
if (TXIF == TRUE && TXIE == TRUE) { // RS232 transmit interrupt
if (xmtoffset != putoffset) { // still data in xmit buffer
x = xmtbuf[xmtoffset]; // next char to xmit
if (++xmtoffset >= XMTBUFSIZE) // update offset
xmtoffset = 0; // wrap
if (xmtoffset == putoffset) // was this last byte?
TXIE = FALSE; // disable xmit interrupts
TXREG = x; // now actually xmit char
}
}
if (RCIF == TRUE && RCIE == TRUE) { // RS232 receive interrupt
if (OERR == TRUE) { // overrun, reset UART
CREN = FALSE; // disable UART
CREN = TRUE; // re-enable UART
} // discard pending bytes
else if (FERR == TRUE) { // framing error (break?)
getoffset = 0; // flush buffers
xmtoffset = 0;
putoffset = 0;
rcvoffset = 1;
rcvbuf[0] = RCREG; // move byte to rcv buffer
CTSinv = TRUE; // ensure CTS is true
}
else { // data without errors
rcvbuf[rcvoffset] = RCREG; // move byte to rcv buffer
x = rcvoffset + 1; // offset next byte
if (x >= RCVBUFSIZE) // beyond buffer boundary
x = 0; // wrap to begin
if (x != getoffset) // buffer not yet full
rcvoffset = x; // update offset,
// (else discard byte,
// CTS flow control failed)
if (CTSinv == FALSE) { // CTS is TRUE
x = getoffset - rcvoffset; // offset difference
if (x <= 0) // wrapping effect
x += RCVBUFSIZE; // wrapping correction
if (x < DELTA) // buffer reaches 'full'
CTSinv = TRUE; // make CTS FALSE
}
}
}
if (INTE == TRUE && INTF == TRUE) { // RB0 change interrupt
// nothing to do, just ..
INTF = FALSE; // .. wake-up from sleep
}
/* Note: Other interrupts disabled, so no further checks needed */
FSR = save_FSR; // restore FSR
int_restore_registers // restore other
}
// -----------------------------------------------
// copy output bytes of caller
// from: application buffer
// to: interrupt controlled transmit buffer
//
// returns nothing
//
// notes: - initiates transmission (interrupt handler)
// when not currently transmitting
// - spin when transmission buffer full
// (wait for free buffer space)
// -----------------------------------------------
static void putdata(char *buffer,
char bytesout) {
char i; // counter(s)
char x; // intermediate byte value
for (i=0; i<bytesout; i++) { // all user data
x = buffer[i]; // copy char
xmtbuf[putoffset] = x; // .. to buffer
x = putoffset + 1; // next char
if (x >= XMTBUFSIZE) // beyond buffer boundary
x = 0;
while (x == xmtoffset) // buffer full!
; // spin until something xmit'd
putoffset = x; // update offset
TXIE = TRUE; // (re-)enable xmit interrupts
}
}
// ----------------------------------------------------------------
// copy input bytes to callers buffer
// from: interrupt controlled receive buffer
// to: application buffer
// returns: number of bytes actually stored in application buffer
//
// notes: - rise CTS when receive buffer has more than <DELTA>>
// bytes free space after delivering data to caller.
// ----------------------------------------------------------------
static char getdata(char *buffer, // application buffer
char bufsize) { // size of appl. buffer
char i, x;
for (i=0; i<bufsize; i++) { // fill user buffer (max)
if (getoffset == rcvoffset) // no more data
break;
x = rcvbuf[getoffset]; // copy char
buffer[i] = x; // .. to user buffer
if (++getoffset >= RCVBUFSIZE) // update offset
getoffset = 0;
}
if (CTSinv == TRUE) { // (CTS is FALSE)
x = getoffset - rcvoffset; // offset difference
if (x <= 0) // wrapping effect
x += RCVBUFSIZE; // wrapping correction
if (x >= DELTA) // enough free space now
CTSinv = FALSE; // (make CTS TRUE)
}
return i; // number of bytes returned
}
// -------------------------------------------------------
// Perform all required initial PIC setup
// -------------------------------------------------------
static void setup() {
CMCON = 0b0000.0111; // Comparator off
CCP1CON = 0b0000.0000; // Capt/Comp/PWM off
OPTION = 0b0000.1111; // WDT prescaler 1:128
T1CON = 0b0000.0001; // Timer1 enabled, presc 1:1
INTCON = 0; // all interrupt bits off
PIR1 = 0; // ..
INTEDG = 0; // int at falling edge RB0
// (= rising of RTS!)
PORTA = 0; // all ports zero
PORTB = 0; // ..
TRISA = 0b0010.0000; // IN: RA5/MCLR
TRISB = 0b0001.0011; // IN: RB0,1,4
PIE1 = 0; // disable all ext. interrupts
BRGH = BPSCLASS; // baudrate class
SPBRG = BPSCOUNT; // baudrate clock divisor
TXEN = TRUE; // enable UART transmit
SYNC = FALSE; // async mode
RCIE = TRUE; // enable receive interrupts
SPEN = TRUE; // enable UART
CREN = TRUE; // enable UART receive
PEIE = TRUE; // enable external interrupts
INTE = TRUE; // RB0 (RTSinv) change
GIE = TRUE; // globally enable interrupts
}
// -------------------------------------------------------------------
// Milliseconds delay by using TMR1 as 16-bits counter
//
// See top of source for the value of TMR1COUNT
// -------------------------------------------------------------------
static void msdelay(char millisec) {
uns16 usTimeCount; // value of Timer1
do {
TMR1H = 0; // restart Timer1 ..
TMR1L = 0; // .. counting
do {
usTimeCount = (uns16)TMR1H << 8; // take high byte value
usTimeCount += TMR1L; // aad low byte value
} while (usTimeCount < TMR1COUNT); // pause 1 millisecond
} while (--millisec > 0); // number of milliseconds
}
// -------------------------------------------------------------------
// Keep PIC in slumbering state: sleep most of the time
//
// Flash a LED as visual 'being alive' signal
//
// -------------------------------------------------------------------
static void waitforRTS(void) {
char ucOptionSave; // option reg at entry
ucOptionSave = OPTION; // save OPTION register
while (RTSinv == TRUE) { // waiting for RTS
OPTION = 0b0000.1111; // WDT postscaler 1:128
sleep(); // wait for RB0 or Watchdog
RTSled = TRUE; // RTS LED on
OPTION = 0b0000.1001; // WDT postscaler 1:2
sleep(); // duration of RTS LED flash
RTSled = FALSE; // RTS LED off
}
OPTION = ucOptionSave; // restore OPTION to original
}
// ===============================================================
//
// M A I N L I N E
//
// Initially CTS is set false and the program waits for
// RTS to become true before activating the echo loop.
// When RTS become true, CTS follows, which allows the
// DTE to send data. The echo loop remains active as
// long as RTS remains true. When RTS becomes false the
// echo-loop is terminated and the PIC reset to its initial
// state, waiting for RTS.
//
// ===============================================================
extern void main(void) {
char i, k, l; // counter(s)
char buffer[20]; // local I/O buffer
const char *welcome = "Echo from S628\n\r"; // welcome!
setup(); // init PIC
for (;;) { // forever
RTSled = FALSE; // assume RTS false
CTSinv = TRUE; // CTS FALSE
waitforRTS(); // in slumbering state
RTSled = TRUE; // show RTS status
CTSinv = FALSE; // CTS TRUE
xmtoffset = 0; // (re-)init ..
putoffset = 0; // .. input and ..
rcvoffset = 0; // .. output ..
getoffset = 0; // .. buffer offsets
for (i=0; welcome[i] != '\0'; i++) { // copy msg to I/O buffer
k = welcome[i];
buffer[i] = k;
}
putdata(buffer, i); // send msg to DTE
while (RTSinv == FALSE) { // RTS true
l = getdata(buffer, sizeof(buffer)); // get input
if (l > 0) // something received
putdata(buffer, l); // echo the input
else // nothing received
msdelay(25); // do 'low priority' work
clrwdt(); // reset watchdog
}
}
}
+
Interested:
See:
Comments:
BUg on lineJames Newton replies: Ah! Very common and annoying error. X is being ASSIGNED the value of RCVBUFSIZE rather then being compaired to it. It should be "if (x==RCVBUFSIZE)" and the best coding style to avoid makeing this mistake is to always put the constant first. E.g. "if (RCVBUFSIZE==X)" becuase if you only put in one "=" the compiler will show you the error.+
if (x = RCVBUFSIZE) // beyond buffer boundary
x = 0; // wrap to begin
note the missing = in the if statement drove me mad for we while!
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