From: ceb <ceb>
Date: Mon, 1 Nov 2004 19:35:54 +0000 (+0000)
Subject: Program to receive data over serial port & write it back out
X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ijackson/git?a=commitdiff_plain;h=b85f6fdc539b4c94d0c30fd499555ea1fe2c0b4b;p=trains.git

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
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