Serial connunications issues...

[ccureau]

I'm having some serial issues, and I'm not quite sure where to go with it.

I've attached two pictures -- one expected output, and one actual output. I've tried changing baud rates and from a WDC 65c51 to a Rockwell 65C51, and both exhibit the same behavior. I don't have another MAX233 to try, but one is on order.

What is really strange is that after the initial patterns, I can type and hold down keys on the keyboard and I get no errors whatsoever. Its almost like it needs a few seconds to get ready...

Pressing the reset button produces the same output. If there were serial errors, I would have expected different output each time.

Has anyone seen something like this before?

EDIT: Forgot to add my code:

Code: Select all

;;
;; Read input from the keyboard, and echo to console.
;;
.PC02

iobase   = $C000
iostatus = iobase + 1
iocmd    = iobase + 2
ioctrl   = iobase + 3

.segment "CODE"
.org $E000

start:		sei		; no interrupts
		lda #$00
		sta iostatus
		lda #$0b
		sta iocmd	; Set command status
		lda #$1e
		sta ioctrl	; 9600,8,N,1

;; print ascii codes
test:
		ldx #$05
loop:		lda #$20
l1:		jsr write
		clc
		adc #1
		bpl l1
		lda #$0d
		jsr write
		dex
		bne loop
		

;; Load a character from the keyboard and store it into
;; the accumulator

getkey: 	lda iostatus   ; Read the ACIA status
        	and #$08       ; Is the rx register empty?
        	beq getkey     ; Yes, wait for it to fill
        	lda iobase     ; Otherwise, read into accumulator
		jsr write
		jmp getkey

;; Write the current char in the accumulator to the console

write:  	
        	;sta iobase     ; write to output.
		;jsr delay_6551
		pha
write1:		lda iostatus
		and #$10
		beq write1
		pla
		sta iobase
		;cmp #$0d
		;bne done
		;lda #$0a
		;sta iobase
		;jsr delay_6551
;done:
		rts

delay_6551:	pha
		txa
		pha
		tya
		pha
		ldy #2		; Clock speed in MHz
minidly:	ldx #61		; lessened from 68 for 1.8MHz
delay_1:	dex
		bne delay_1
		dey
		bne minidly
		pla
		tay
		pla
		tax
		pla
		rts
		
; system vectors

.segment "VECTORS"
.org    $FFFA

.word   start       ; NMI vector
.word   start       ; RESET vector
.word   start       ; IRQ vector

[BigEd]

Oddly enough it looks more like a parallel issue - it looks like bit 1 is unreliable. The sequence
012345678
is mutating to
030347678
and that's always a flip of bit 1. Similarly for the alphabets.

Is the databus side of the socket for your serial chip well-connected?

(What kind of computer are you running? What kind of construction technique?)

[ccureau]

Ed,

Its all on a breadboard...and all run through a single 1.8MHz oscillator. It sounds like you are saying that D0 might be bad?

[BigEd]

It's almost like D1 (which is bad) is getting the value of D0.
Edit: but not exactly that. Some of the sequences are coming out slightly different from each other.

[ccureau]

Ed, you're a genius! I replaced D0 and D1 and it works a charm Thanks!

[BigEd]

That's great!

[GARTHWILSON]

Note that you can simplify your code too, since you're using the CMOS processor.

• LDA #0, STA can be replaced with STZ.
• TXA, PHA can be replaced with PHX.
• TYA, PHA can be replaced with PHY.
• PLA, TAX can be replaced with PLX.
• PLA, TAY can be replaced with PLY.
• CLC, ADC #1 can be replaced with INC A (alias mnemonic being INA).
• SEI can be eliminated from the beginning of any reset or interrupt-service routine, since setting the interrupt-disable bit is already an implied, automatic part of the sequences. (This is true of NMOS too.)

[ccureau]

Hi Garth,

Thanks for your thoughts...I hadn't really gotten to optimizations yet for two reasons: I've built a target with SyMon, which only supports NMOS 6502 instructions; and I haven't really looked at the 65c02 instructions yet, as I come from assembly with my trusty C64 and C128. I just wanted something to prove that the thing worked...the quality will come soon.

I built a new target in cc65 for my board...I love how easy Uz made it to target a new board! Many kudos to him and to Oliver for maintaining and extending it!