Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 303)

Chapter 15
Using Communication Protocols
15–19
Rung 2:1
The Time Out bit (TO) associated with each message instruction is used to
clear the controllers communication buffer and message instruction.
Setting these bits, basically places the controllers communication section
in the same condition as when the controller power up. These bits allow
control program to reset or recover from unexpected events (e.g., errors,
power problems, media problems).
| Message Error Write Message |
| Retry Timer Time Out |
| T4:9 N7:50 |
|––––––] [–––––––––––––––––––––––––––––––––––––––––+–––( )––––––––––+–|
| DN | 8 | |
| | Read Message | |
| | Time Out | |
| | N7:60 | |
| +––––( )–––––––––+ |
| 8 |
Rung 2:2
Write message with preceding logic. It is STRONGLY recommended that bit
S2:0/11 (active protocol bit) be used to condition all message
instructions. This bit only allows the message instruction to operate
when the correct protocol is active. The read message enabled bit
(N7:60/15) is used to “open” the rung of the write message when the read
message is active. This sequences the write message to proper state,
allowing immediate transmission when the read message completes its
operation. NOTE: If DF1 was the protocol used by the message
instruction, use –]/[– S2:0/11 for the preceding logic.
| DH-485 Active Read Message Write Message Ins. |
| Enabled |
| S2:0 N7:60 +MSG–––––––––––––––––––––+| |
|–––] [–––––––––––––––]/[––––––––––––+Read/Write Message +–(EN)+–|
| 11 15 |Read/Write Write+–(DN) |
| |Target Device 500CPU+–(ER) |
| |Control Block N7:50| |
| |Control Block Length 7| |
| | Setup Screen | |
| +––––––––––––––––––––––––+ |
Rung 2:2
Write message with preceding logic. It is STRONGLY recommended that bit
S2:0/11 (active protocol bit) be used to condition all message
instructions. This bit only allows the message instruction to operate
when the correct protocol is active. The write message enabled bit
(N7:50/13) is used to enable the read message as soon as the write message
completes its operation. NOTE: If DF1 was the protocol used by the
message instruction, use –]/[– S2:0/11 for the preceding logic.
| DH-485 Active Read Message Read Message Ins. |
| Enabled |
| S2:0 N7:50 +MSG–––––––––––––––––––––+| |
|–––] [–––––––––––––––] [––––––––––––+Read/Write Message +–(EN)+–|
| 11 13 |Read/Write Read+–(DN) |
| |Target Device 500CPU+–(ER) |
| |Control Block N7:60| |
| |Control Block Length 7| |
| | Setup Screen | |
| +––––––––––––––––––––––––+ |