应用现场是：

S7-400 PLC，416-2DP；

通过PN口连接PNPN coupler。

经常会显示下面的故障：

Event 120 of 120:  Event ID 16# 39B4

I/O access error when updating the process image output incoming

Access error occurred with user data 

Process image partition no.:  0

Start address of I/O area involved:   1000, Length of the area: 196 

Requested OB: Program execution error OB (OB85)

Priority class: 25

External error, Incoming event

11:23:06.918 AM  02/26/2016

(Coding: 16# 39B4  1955  5750  2943  00C4  03E8)

Event 118 of 120:  Event ID 16# 3942

Module problem or maintenance necessary

Module type: Distributed I/0s

Input address: 16372

Channel information available

User information available 

Module/submodule fault

External module error

Channel error detected

Requested OB: Diagnostic interrupt OB (OB82)

Priority class: 25

External error, Incoming event

11:23:06.936 AM  02/26/2016

(Coding: 16# 3942  1952  C554  3FF4  0D33  0000)

然后模块又自动恢复：

Event 117 of 120:  Event ID 16# 3842

Module OK

Module type: Distributed I/0s

Input address: 16372

Channel information available

Requested OB: Diagnostic interrupt OB (OB82)

Priority class: 25

External error, Outgoing event

11:25:21.197 AM  02/26/2016

(Coding: 16# 3842  1952  C554  3FF4  0013  0000)

今天发生的频率上升，并且导致CPU停止。

Event 25 of 120:  Event ID 16# 494D

STOP due to IO error 

No relevance for user (Z1): 9182

No relevance for user (Z2): 03b0 (Z3): 04f9 

Previous operating mode: RUN 

Requested operating mode: STOP (internal)

External error, Incoming event

不知道大家是否遇到类似问题。

是不是有什么方法可以解决这个问题？

希望大家能给予指导。