serial comm problem

[mister_e]

no big solution... it's working here using

Private Sub Form_Load()
    Option1(0).Value = True
    MSComm1.CommPort = 1
    MSComm1.Settings = "2400,n,8,1"
    MSComm1.DTREnable = False
    MSComm1.RThreshold = 1
    MSComm1.InputLen = 1
    MSComm1.PortOpen = True
End Sub
Private Sub Command1_Click()
    Dim pinstate As Byte
    If Option1(0).Value = True Then
        pinstate = 1
        Else
            pinstate = 0
        End If
    
    MSComm1.Output = Chr(255) & Chr(pinstate)
End Sub

Private Sub form_unload(Cancel As Integer)
    MSComm1.PortOpen = False
End Sub

on the PICSide

INCLUDE "modedefs.bas"

Si       VAR PORTA.4
RELAY    VAR PORTB.2
pinstate VAR BYTE

main:
    SerIn Si,n2400,[255],pinstate
    
    IF pinstate=1 Then
        GoSub Relayon
        Else
           GoSub Relayoff
        EndIF
    
    goto main
    
Relayon:
    High RELAY
    Return

Relayoff:
    Low RELAY
    Return

sorry, try a lower resistor value and be sure you share the same ground, be sure you place 0.1 uF cap close to your PIC and be sure of your crystal speed and capacitor value.

Schu4647 have also point an interesting fact... be sure it's not the relay who create the bug.