Wait for a string on a serial port

[RuudNL]

I am having a problem receiving data from a serial port.
In fact, the serial port receives MIDI information, it is no problem to set the baud rate to the midi standard of 31,25 KHz.

What I need is the following.

The sequence of CHR(176) + CHR(44) + CHR(69) should turn a port pin 'on'
The sequence of CHR(176) + CHR(44) + CHR(5) should turn a port pin 'off'

While this is running, a random combination of characters may appear on the input, but this should not influence the status of the output pin used.
The output should only react on 176+44+69 AND 176+44+5
I have made something already, but it seems this is not reliable.
Any ideas? Suggestions are highly appreciated!

[aerostar]

your code would be helpful but here is a pointer

pinon VAR portX.Y 'eg portb.7

Pollmidi:
HSERIN [WAIT(176,44),variable]
if variable = 69 then pinon=1 'alias to port
if variable = 5 then pinon =0
goto Pollmidi


Note there is no get out of this loop but this should give you an idea.

SERIN should also work if you do not have hardware UART

[RuudNL]

Thanks! That may be useful. I didn't know that you could combine a fixed string and a variable when using WAIT.
(I always thought you only could use a fixed string here.)

[RuudNL]

I just tested it, and it works.
At first I got the impression that is was unreliable (to the same degree as what I had created), but after some experimentation it showed that I needed a pull-up resistor at the output of the MIDI port. (In fact you should use an optocoupler for this.)
But with a pull-up resistor it works now without any problems. So I think my code would work also, but this code is more compact, so I will keep using it.
Many thanks again!

[Scampy]

This is the code I use for my serial comms

RCIF                VAR PIR1.5                    ' USART receive flag
Char                VAR BYTE                      ' USART byte received
GIE                 VAR INTCON.7 
nTest               var byte

and then in the main loop of the code

FOR TempWD = 0 TO 500
    IF RCIF=1 THEN GOSUB coms                   ; Check to see if PC application connected
    PAUSE 1
next TempWD

And then the Comms subroutine

HSERIN [nTest]
    SELECT CASE nTest
    CASE "Q"                    ; if Q then send data to PC
    Goto Term_TX 
    CASE "S"                    ; if S then receive data from PC
    goto Term_RX
return

The Term_RX / Term_TX subroutines are then used with HSERIN or HSEROUT to receive and send data. As can be seen from the code I use Q and S as the keys to communicate with a PC application which receives variable data and populates text boxes, or if the value are changes in those text boxes and the update button clicked, the PS sends the new values for the variables..

Hope that helps

[Art]

With just a 3 byte buffer the whole thing could be non blocking,
and the 1 timeout might even be able to be changed to zero for no delay at all.

buffer var byte[3]
inputbyte var byte

main:
'
HSERIN 1,nodat,[inputbyte]	‘ receive next byte
buffer[2] = buffer[1]		‘ rotate into buffer
buffer[1] = buffer[0]
buffer[0] = inputbute
if (buffer[2] = 176 && buffer[1] = 44) then
if buffer[0] = 69 then portb.0 = 1
if buffer[0] = 5 then portb.0 = 0
endif
nodat:				' timeout label for no byte received
'
// the rest of the program
‘
goto main