Technical data

Opening a page
Operation Operand Explanation
ACR Open the page whose number is
located in ACCU-1-L
permitted values: 0 to 255
Error reaction The page number must be between 0 and 255. If this is not the case,
the CPU recognizes a runtime error and calls
OB 31, providing it is
loaded. If OB 31 is not loaded, the CPU goes to the stop mode.
In both cases, error IDs are entered in ACCU-1-L, that define the error
in greater detail (see Section 5.6.2).
Testing and setting a busy
location in the page area
You can control the access of individual CPUs to common memory
areas using a busy location. Each memory area used by more than one
CPU has a busy location assigned to it that must be tested by each
CPU before it can access this area. The busy location either contains
the value "0" or the slot identifier of the CPU currently using the
memory area. This CPU releases the memory area by
writing "0" to
the busy location again when it is finished.
(Note the explanations
of the operations "set semaphore/SED" and "enable semaphore/SEE"
in Section 3.5.5.).
The CPU tests and sets a busy location on the open page using the
TSC operation.
Operation Operand Explanation
TSC -32768 to
+32767
Add the specified constant to the
content of the BR register and test and
set the location on the opened page
addressed in this way.
Sequence The low byte of the word addressed by the contents of the BR register
+ the constant is used as the busy location. If the content of the low
byte is "0", the TSC operation enters the slot ID (from RS 29) into the
busy location.
Testing (= reading) and setting (= writing) the busy location is one
program unit that cannot be interrupted.
Operations with the Base Address Register (BR Register)
CPU 928B Programming Guide
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