Opening a dual-port RAM
page
Operation Parameter Description
ACR Open the dual-port RAM page whose
number is located in ACCU-1-L ,
permissible values: 0 to 255
The dual-port RAM page number must be between 0 and 255. If it is not,
the CPU detects a substitution error (SUF) and calls OB 27. If OB 27 is
not loaded, the CPU changes to the STOP mode.
Testing and setting an
"occupied" register in
the dual-port RAM area
You can control access of individual CPUs to commonly used memory
areas by using an "occupied" register. An "occupied" register is assigned
to each commonly used memory area. Each participating CPU must test
this register before accessing the memory area. The "occupied" register
contains either the value ’0’ or the slot ID of the CPU that is presently
using the memory area. When the CPU is finished using the memory
area, it writes ’0’ to the "occupied" register to re-enable the memory
area. (Note the explanations of the operations "set semaphore/SED" and
"enable semaphore/SEE" in Section 3.5.5.)
The TSC operation handles the testing and setting of a location on the
open page.
Operation Operand Description
TSC -32 768 to
+32 767
Add the specified constant to the content
of the BR register and test and set the
location addressed in this way on the
open page.
Sequence
The low byte of the word addressed by the sum of the BR register +
constant is used as the "occupied" register. If the low byte contains
’0’, the TSC operation enters the slot ID of the CPU in the "occupied"
register.
Testing (reading) and possible occupation (writing) form a program
unit that cannot be interrupted.
Operations with the Base Address Register (BR Register)
CPU 948 Programming Guide
9 - 30 C79000-G8576-C848-04
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