;----------------------------------------------------------------------; ;ALPHA4M.ASM Sends and receives characters serially 4800 baud with PC ; ;----------------------------------------------------------------------; ; A terminal program runs on the PC set to 4800 baud, 8 bit, no parity ; 1 stop bit no handshaking. When a character is typed on the keyboard ; it is sent to the PIC and the PIC returns the next 3 ASCII characters ; .-----------. ; -|RA2 RA1|--------[DB9S pin 2] ; -|RA3 RA0|----{R}--[DB9S pin 3] ; -|RA4 OSC1|--|X|___ gnd ; V+ ---|MCLR OSC2|--|X| ; gnd ---|Vss Vdd|--- V+ -{R}- = 22 K resistor ; -|RB0 RB7|- X = 4 MHz cer. res. ; -|RB1 RB6|- V+ = 4.5 or 5 Volts ; -|RB2 RB5|- ; -|RB3 RB4|- ; '-----------' ; PIC16F84 ; DB9S female com port connections: ; pins 1, 4 and 6 connected together (DCD,DTR & DSR) ; pins 7 and 8 connected together (RTS & CTS) ; pin 5 to gnd ; pin 2 to PIC pin 18 (RA1) ; pin 3 to 22 K resistor to PIC pin 17 (RA0) LIST P=16F84 ; tells which processor is used INCLUDE "p16f84.inc" ; defines various registers etc. Look ERRORLEVEL -224 ; supress annoying message from tris __CONFIG _PWRTE_ON & _XT_OSC & _WDT_OFF ; config. switches #DEFINE incom PORTA, 0 ; input port #DEFINE outcom PORTA, 1 ; output port CBLOCK H'0C' txreg ; holds byte to be transmitted rxreg ; holds byte received char ; holds character to be transmitted bitcount ; holds count of bits when transmitting cntmsec ; holds counter for milliseconds ENDC ORG 0 ; start a program memory location zero goto main ; skip over subroutines ;----------------------------------------------------------------------; ; initialization - set up ports and timer options ; ;----------------------------------------------------------------------; init: movlw B'00000001' ; RA0 to input tris PORTA ; contents of W copied to PORT A ... movlw B'0000000' ; all of PORT B outputs tris PORTB return ;----------------------------------------------------------------------; ; time delay routines ; ;----------------------------------------------------------------------; bitdelay movlw D'51' ; one bit period at 4800 baud ; 50 * 4 + 5 + 1 + 2 = 208 usec ; for 'call bitdelay' ; Timing is determined by counting instruction cycles. ; micro4 is a loop that take 4 microseconds each time through, ; (4 mhz crystal). By using W, you save a general register. ; The last time through take 5 microseconds, including the return. ; If W is 248 on entry the total time is 247 * 4 + 5 = 993 usec. ; An additional 2 usec for the call gives 995 microseconds. ; The instruction 'call micro4' in this case represents 995 usec. micro4 addlw H'FF' ; subtract 1 from 'W' btfss STATUS,Z ; skip when you reach zero goto micro4 ; more loops return ;*** N millisecond delay routine *** msec250: movlw D'250' ; 250 millisecond delay nmsec: movwf cntmsec ; delay for N (in W) millisec msecloop: movlw D'248' ; 1 usec for load call micro4 ; this instruction is 995 usec nop ; 1 usec decfsz cntmsec,f ; 1 usec, (2 if skip taken) goto msecloop ; 2 usec, loop = 995+5 = 1 msec return ;----------------------------------------------------------------------; ; the main program ; ;----------------------------------------------------------------------; main: ; this is the main program call init ; set up ports call msec250 ; let things settle loop: call rx movwf char incf char, f movf char, W call tx incf char, f movf char, W call tx incf char, f movf char, W call tx goto loop ;----------------------------------------------------------------------; ; transmit byte in W at 4800 baud to PC ; ;----------------------------------------------------------------------; ; normal rs232 is -V for a high, +V for a low ; this would translate to 0V for high +5 for low ; a bit length at 4800 baud is 208 microseconds ; this is made up of a delay of 199 microseconds, (call micro4), plus ; 9 or 10 microseconds taken up with instructions in each txloop tx: movwf txreg ; put W into transmit register movlw D'08' ; eight bits of data movwf bitcount ; a counter for bits bsf outcom ; start bit (flipped remember) txloop: movlw D'49' ; delay time call micro4 ; wait 48*4+5+2 = 199 microsec rrf txreg, f ; roll rightmost bit into carry btfsc STATUS, C ; if carry 0, set bit (a low) goto clrbit ; else clear bit, (a high) bsf outcom ; +5V on output pin goto testdone ; are we finished? clrbit: bcf outcom ; 0 volts on output pin testdone: decfsz bitcount, f ; one less data bit, skip when 0 goto txloop ; more bits left, delay this one call bitdelay ; delay for last data bit bcf outcom ; 0V, ( a high ) for stop bits call bitdelay ; 2 stop bits call bitdelay return ;----------------------------------------------------------------------; ; receive byte at 4800 baud from PC, put in W ; ;----------------------------------------------------------------------; rx: startbit: btfss incom ; goes high for start, (reversed) goto startbit ; not yet wait some more movlw D'24' ; wait half a bit time call micro4 ; btfss incom ; check if still high goto startbit ; no, start again movlw D'8' ; 8 bits movwf bitcount ; into counter clrf rxreg ; clear out register receive: movlw D'49' ; makes call micro4 = 199 usec call micro4 ; wait one bit length (- instr.) bsf STATUS, C ; start with high to shift in btfsc incom ; if pin low, shift in high (rev) bcf STATUS, C ; else change to low rrf rxreg, f ; shift bit in decfsz bitcount, f ; last bit collected? goto receive ; not yet, get more, 8 usec+call call bitdelay ; stop bit movf rxreg, W ; result into W return end
file: /Techref/piclist/cheapic/alpha4m.asm, 8KB, , updated: 2000/12/7 16:49, local time: 2024/8/31 16:48,
3.14.141.128:LOG IN
|
©2024 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions? <A HREF="http://massmind.org/techref/piclist/cheapic/alpha4m.asm"> piclist cheapic alpha4m</A> |
Did you find what you needed? |
Welcome to massmind.org! |
Welcome to massmind.org! |
.