serial communication time

[Mugelpower]

Hi Guys & Girls!

my serial data transfer between two pics 16F628A works for starters. BUT: in my program theres at high engine speeds only 0.4 ms or less to send the data from one pic to another.
The action my receiving PIC makes is triggered by an external interrupt that means after that theres hardly time to get the data. On the other hand it doesn´t matter if it misses the data for a few cycles because at high engine speeds the data update could wait . I think it is sufficient to transmit that data every 0.1 sec.

Yes: baud rate 9600, 4 Mhz crystal, data: one word. Input Frequency 3 Hz - 600 Hz

Does this work?

on Interrupt goto ISR

main:
serin2 blah blah

isr:
pulsout 7, 50, 1

something like that




I will show the program when i´m back home

AH: one BIG Problem too:
when using a 2-channel oscilloscope it shows a Delay between input signal and output signal
of about 0.5 ms more than expected. this makes the whole action too slow!!!
Maximum accepted delay between input trigger and output pulseout could be 0.1 ms.

is the only way to handle those timecritical events by assembler? please say no....

Mugel

[skimask]

only 0.4 ms or less to send the data from one pic

I think it is sufficient to transmit that data every 0.1 sec.

9600 baud = 9600 bits per second
1 second / 9600 = .1046 ms per bit
1 byte = 8 bits + start bit + stop bit = 10.5 bits
10.5 x .1046 = 1.0983ms per single data byte = 910.498 bytes per second MAX

The math doesn't work...

[paul borgmeier]

Mugel,

It is not clear to me what you are trying to do. If you use the Hardware USART, you can send and receive in the "background" and keep your programs doing what they need to do.

Further, are you using RS232? Why Pulsout shown in the ISR?

More details = more help

[Mugelpower]

oha,
1 ms for Data transfer is way too much. And recieving data (no sending!) in the background seems the only thing to do
'************************************************* *******************************************
' 16F628A 10 Mhz crystal 15pf capacitors
' damn program should blink an LED every time a pulse goes into RB.0
' later a value should be serial loaded and set a delay before the blink pulse
'************************************************* *******************************************

'
' DEFINITIONS


DEFINE OSC 10
CMCON=%00000111
inputData var word ' variable to receive data into
pulseWidthVar var word



' START OF MAIN PROGRAM
'
CMCON = 7 ' RA0-RA3 are digital I/O
TRISA = 0 ' PORT A is output
TRISB = 1 ' RB0 is Input others output


on interrupt goto ISr

INTCON.1 = 0 ; Clear External Interrupt Flag
INTCON.4 = 1 ; Enable External Interrupt



main:
Portb.7 = 0

serin2 portB.0,16468, [inputData] 'for the future to load a value
pulseWidthVar = inputData

goto main

disable

ISR:

portb.7 = 1 'blink LED 0.02 sec one time when RB.0 goes high
pauseus 500
portb.7 = 0
INTCON.1 = 0 ; Clear External Interrupt Flag
RESUME 'resume main program
Enable 'Enable interrupts

END ' End of program

In my picbasic pro book from Dogan Ibrahim it says " USART is very complicated"
and that did not encourage me.
Because I use only 16F628A , maybe with 10Mhz that should do.

How could I use the Usart . I think those 16F628A have one....

[mister_e]

Then throw that book away

HSERIN is one, method. Reading the USART register is another one, using it's interrupt is a third one.

Now you have to determine which process is much important. If you really have a need for speed for your interrupt, you may need to switch to Darrel's Instant-Interrupt. Not enough? ... use ASM interrupts.

@10MHz, you could use a 57600 baud communication without too much problem.

Not sure of your whole requirement... but i would use USART interrupt for that... i'll read it again.. just to make sure i didn't miss the main idea.

[Mugelpower]

Hi Mister_E,

you helped me a lot last time I remember. OK. Principle is an Ignition that gets an input signal (raising edge on Portb.7) , starts an interrupt and after a "Delay" it sends a 0.5 ms High to an Output. After that it recieves serial the actual variable "Delay" which is a byte and is ready for the next interrupt.
This all in about 1.5 ms at maximum speed.
I have a second PIC that measures pulse width and calulates "Delay" so I save Time and code for the time critical Interrupt.

But the Delay caused by the PBP program including the serial communication is about 1ms thats way too much.