Siemens SIMATIC S5 CP 523 Manual page 87

Print Mode
Function of the message buffer
The CP 523 is equipped with a message buffer. Job requests to the printer (print requests) are
stored in this message buffer. The CP forwards the print requests to the printer from the message
buffer. The print requests are sent in the same order as they are received from the CPU (FIFO).
The print request is deleted in the message buffer once the CP 523 has serviced it. If the CPU sends
a large number of print requests within a short time, the number of pending requests will in-
crease. If there are 255 job requests waiting to be serviced and the CPU sends another request, the
CP 523 cannot process this last request. In this case, the CP 523 flags "Job/message buffer full"
(08 ) to the CPU in byte 0 "Status of the module".
H
The CP reports "Job / message buffer full" 08
1. The job buffer is full because more than 31 print requests have been sent consecutively from
the CPU to the CP (CPU faster than CP).
2. The message buffer is full because more than 255 print requests are waiting to be serviced
(CPU and CP faster than printer).
Note:
If you have to issue a large number of print requests within a short period, check to make sure
that the message buffer still has capacity.
- See 6.6 for a description of how to proceed when checking the message buffer.
6-32
in the following two cases:
H
CP 523
EWA 4NEB 811 6044-02a