Why does my serial interrupt code not work?

[AceOfHearts]

Hi,

Basically, I am creating a remote control interface for my robot. I am trying to get the serial interrupt to work. In the code below, Keypad uC system (now simulated by PC) sends 0 in binary when the turn right key is pressed on the remote control, 9 is sent for turn left key.

The robot program should be haulted when a serial byte comes in, and checks to see what value it receives, and jumps to turn right, left etc. appropriately depending on what the received byte is.

Though my code compiles, it does not work when I download it onto the 8051 on my robot. When I run it for the first time on the 8051, upon the first byte input, the uC simply goes back to the top of the program and starts again (like I have reset it). Any subsequent presses on any key makes no affect on the robot, it just functions normally ignoring all serial data input.

Here is the code:

**broken link removed**

Note: comment reads 'interrupt service routine' next to ORG 23H at the beginning of the code. Thats obviously not the ISR, it's at the bottom (just not to confuse beginners reading). Also, 'now clear it' in comment next to CLR RI

Looking forward to any help anyone has to offer.

Thanks for reading.

 

[mneary]

You should CALL the routines RIGHT and START (and return from them) so you can RETI properly.

 

[AceOfHearts]

You should CALL the routines RIGHT and START (and return from them) so you can RETI properly.

I see.

I had to edit and re-edit few times.

I get what you mean. Thanks for much!! I appreciate it. I will give that a go.

 

[AceOfHearts]

You should CALL the routines RIGHT and START (and return from them) so you can RETI properly.

Ive got one more question, do I need to RETI from those CALLs I make in ISR or just RET?

thanks.

 

[mneary]

you just need RET

 

[AceOfHearts]

Thanks.

It still doesnt work

I just dont know what I am doing wrong now!

 

[AceOfHearts]

Anyone else ever worked with serial interrupt on the 8051?

The problem I am having is that when I send a byte, the program goes back to the top and starts again. Any subsequent byte sent is ignored by the progrem, unless I reset the uC, then the same thing happens....

 

[mcs51mc]

This is how I did it once

I didn't use the interrupt but polled the RI and TI bits.
I transmit packages of 5 bytes between PC and µC.
You can see the variable "Scherm" as a state of a state machine:
During state 80, 5 bytes are received from the PC
During state 81, 5 bytes are send to the PC

Below code for:
1) Init serial comm
2) Receive 5 bytes from PC
3) Send 5 bytes to PC
4) Stop serial comm


1) Initialising serial comm

;	Setup the serial port for 4800 baud at 12MHz.
;	TH1 = 256 - (crystal / (2 * 12 * 16 * baudrate)) with SMOD.7 = 0
;	TH1 = 256 - (crystal / (12 * 16 * baudrate))     with SMOD.7 = 1
;		with crystal= crystalfrequentie (Hz)
;		baudrate= desired baudrate (bits/sec)
;
InitializeSerialComm:
	mov  SCON,#050h		;SCON: mode 1, 8-bit UART, enable rcvr
	orl  PCON,#080h		;Set bit SMOD.7 to doubles the baud rate
	orl  TMOD,#020h		;TMOD: timer 1, mode 2, 8-bit reload
	mov  TH1,#0F3h		;TH1:  reload value for 4800 baud @ 12MHz
	setb TR1			;TR1:  timer 1 run
	setb TI			;TI:   set TI to send first char of UART
	ret

2) Poll RI bit and if set, store received byte in array and when 5 bytes are received, handle them.

L6080A:	jnb  RI,L6080End			;Wait until character received
			
	mov  a,#SerialData		;Calculate address for received byte
	add  a,GP_Array+6
	mov  R0,a
	mov  @R0,SBUF			;Store received byte
	clr  RI				;Clear reception flag
			
	inc  GP_Array+6
	mov  a,GP_Array+6			;5 bytes received?
	xrl  a,#5
	jnz  L6080End

	jmp  HandleReceivedBytes
L6080End:ret

3) Send 5 bytes to PC

L6081Start:	cjne a,#81,L6082Start		;Scherm 81
		jnb  TI,L6081End			;Wait until transmission complete
		clr  TI				;Clear 'Ready for transmission' flag

		mov  a,#SerialData		;Calculate address for byte to send
		add  a,GP_Array+6
		mov  R0,a
		mov  SBUF,@R0			;Send byte
			
		inc  GP_Array+6
		mov  a,GP_Array+6			;5 bytes send?
		xrl  a,#5
		jnz  L6081End
			
		mov  Scherm,#82			;Naar scherm 82: Ontvangen data schakeltijden
L6081End:	ret

4) Stop serial comm when not needed any more:

		clr  TR1				;Stop serial comm  TR1:  timer 1 run

 

[AceOfHearts]

Thanks very much, interesting indeed.

I am trying the polling method, though even that is not working. I will continue to check where I am going wrong

 

[AceOfHearts]

Ok polling worked. I will stick with this for the time being.

 

[mcs51mc]

Nice to hear that !
Can you also tell us what was wrong so that we all can learn of it ?
Thanks a lot for that...

 

[AceOfHearts]

Nice to hear that !
Can you also tell us what was wrong so that we all can learn of it ?
Thanks a lot for that...

Hi,

The polling interrupt wasnt working I think because of 'silly' mistakes and not because of errors in the way I was polling. I had JUMPS to routines where I had placed RET thinking they were CALLS, of that sort basically.

I take it that polling is more reliable/easy to work with (particularly serial interrupt)? I was reading www.8052.com which said something like interrupt codes are easy to mess up, the program may run for a while and then crash - maybe even after a month etc. if you dont get things thought out properly/spot on etc.

 

[Nigel Goodwin]

I take it that polling is more reliable/easy to work with (particularly serial interrupt)? I was reading www.8052.com which said something like interrupt codes are easy to mess up, the program may run for a while and then crash - maybe even after a month etc. if you dont get things thought out properly/spot on etc.

I wouldn't say it's any more reliable, just that if you don't program it correctly it's easy to make stupid, very difficult to find, mistakes.

If you're not confident using polling, you probably shouldn't be attempting interrupts until you've become more competent.