Program to receive data over serial port & write it back out

main loop flashes LED green
uses interrupts to start off serial read/write; LED red whilst in interrupt routine

diff --git a/cebpic/reply-serial.asm b/cebpic/reply-serial.asm
new file mode 100644 (file)
index 0000000..ed567eb
--- /dev/null
+++ b/cebpic/reply-serial.asm
@@ -0,0 +1,100 @@
+; pin 21 (per-pic-led, RD2/PSP2/C1IN) states: high H = green, low L = red, float Z = black
+
+        include         /usr/share/gputils/header/p18f458.inc
+
+       code
+
+       goto    initialise_serial
+
+
+; interrupt routine call - this needs to be at 000018h (low priority interrupt)
+
+       goto    interrupt_check
+
+
+initialise_serial
+
+; initial config - TXSTA register p181
+        bcf     TXSTA,6,0      ; p181, set 8-bit mode
+       bsf     TXSTA,5,0       ; transmit enable
+       bcf     TXSTA,4,0       ; asynchronous mode
+       bsf     TXSTA,2,0       ; set high baud rate
+       
+; initial config - RCSTA register p182
+        bsf    RCSTA,7,0       ; serial port enable (p182)
+       bsf     RCSTA,6,0       ; 8-bit reception
+       bsf     RCSTA,4,0       ; enable continuous receive
+
+; set SPBRG to get correct baud rate according to table top right p186
+; (Tosc = 20MHz, desired baud rate = 9600)
+       bsf     SPBRG,7,0
+       bsf     SPBRG,0,0
+
+; interrupt set-up for serial receive
+       bsf     PIE1,5,0        ; enable USART receive interrupt (p85)
+       bsf     IPR1,5,0        ; set to low-priority interrupt
+
+
+; LED pin (21) initialisation
+        bcf     TRISE,4,0       ; turn off PSPMODE (Data Sheet p100/101)
+
+
+; timer0 initial config
+        bcf     T0CON,6,0       ; p107 Timer0 -> 16bit mode
+        bcf     T0CON,5,0       ; timer0 use internal clock
+       bcf     INTCON,5,0      ; clear TMR0IE => mask interrupt
+        bcf     T0CON,3,0       ; use prescaler
+        bcf     T0CON,2,0       ; }
+        bsf     T0CON,1,0       ; } prescale value 1:8 (13ms x 8)
+        bcf     T0CON,0,0       ; }
+
+
+main
+       call    led_green
+        call    waiting
+       call    led_black
+        call    waiting
+       goto    main
+
+
+led_green
+        bcf     TRISD,2,0       ; make pin RD2 an output (DS100)
+        bsf     LATD,2,0        ; set pin RD2 H (green)
+        return
+
+led_black
+        bsf     TRISD,2,0       ; make pin RD2 an input (i.e. set Z, black) (DS100)
+        return
+
+led_red
+        bcf     TRISD,2,0       ; make pin RD2 an output (DS100)
+        bcf     LATD,2,0        ; set pin RD2 L (red)
+        return
+
+
+waiting
+        bcf     INTCON,2,0      ; clear timer0 interrupt bit (p109)
+        clrf    TMR0H,0         ; p107 set high bit of timer0 to 0 (buffered,
+                                ; so only actually set when write to tmr0l occurs)
+        clrf    TMR0L,0         ; set low bit o timer0 - timer now set to 0000h
+loop
+        btfss   INTCON,2,0      ; check whethr tiomer0 interrupt has been set -
+                                ; skip next instruction if so
+        bra     loop
+        return
+
+
+
+
+interrupt_check
+       btfss   PIR1,5,0        ; check whether serial receive interrupt bit set
+       retfie                  ; return from interrupt to main if spurious interrupt
+       call    led_red
+       clrf    WREG            ; clear working register
+       movff   RCREG,WREG      ; read data out of serial receive buffer -> WREG
+       incf    WREG            ; increment WREG
+       movff   WREG,TXREG      ; write data out of WREG -> serial transmit buffer
+       retfie
+
+
+       end