CP 523
Print Mode
Access to the CP 523 transfer memory
The CPU can read the transfer memory at any time with L PW statements and write to it with T PW
statements.
The CP 523 must be able to detect the instant at which the data transferred by the CPU is valid.
Data in the transfer memory is recognized as valid by the CP 523 whenever the CPU transfers a
(print) request in word 0 of the transfer memory. As soon as word 0 has been written, the CP 523
evaluates all the transfer memory data and overwites it with the current data (words 0 to 6).
This has the following consequences for the order in which data is transferred from the CPU to the
transfer memory:
•
First, words 2, 4 and 6 in the transfer memory must be written if the job request requires it. If
you want to print a message text into which three variables are to be inserted, for example,
the current values must be transferred to words 2, 4 and 6.
•
Finally, the job number must be written into word 0 of the transfer memory (special feature of
the CPU 944 5.2).
If you do not adhere to this order, the new job request will be executed with the wrong values.
+ Function of the job buffer
The CPU stores print requests in the job buffer immediately without checking them (a full eight
bytes from the transfer memory in each case). The CP then empties the job buffer into the message
buffer. It can happen that the CPU updates the transfer memory faster than the CP writes requests
from the job buffer into the message buffer. The number of job requests in the job buffer in-
creases as a result of this. The job buffer can hold a maximum of 31 job requests. Additional
requests cannot be accepted. The CP reports "Job buffer full" (08
H
) in the transfer memory. This
can happen if you send more than 31 print requests consecutively to the CP.
If you nevertheless want to send more than 31 print requests, you can proceed in one of the
following ways:
•
Scan the status of the module for "Job buffer empty?" (03
H
) after 31 print requests. If the CP
stores this response (00
H
) in the status byte, you can send a further 30 requests.
•
If the "Entries already in the job buffer" message (03
H
) appears, you can issue at least one
further print request.
•
Scan the status of the module for "Job buffer full?" (08
H
) after 31 print requests. If the CP
stores this response in the status byte, the job request must be reissued.
EWA 4NEB 811 6044-02a
6-31
