| 1. | 
                                   GP displays B1. | 
                                
                                
                                  |  At that time, the currently displayed screen number, [1] is stored in +0 of the system data area. | 
                                
                                
                                  | 2. | 
                                   Write the change destination screen number, [2] in +8 of the system data area from PLC side. | 
                                
                                
                                  | 3. | 
                                   GP displays B2. | 
                                
                                
                                  | 4. | 
                                  The screen is changed to B3 via a touch switch (a special SW etc.) of GP. | 
                                
                                
                                  | [3] is stored in +0 of the system data area. | 
                                
                                
                                  |  *In this case, a screen number is not written in +8 of the system data area. +8 is still 
[2]. | 
                                
                                
                                  | 5. | 
                                   Write [2] in +8 of the system data area. | 
                                
                                
                                  |  Since [2] has already been in +8 of the system data area, screens don’t change. | 
                                
                                
                                  |  *GP is watching changes of data and [2]->[2] means no change. |