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BUS Test and Set
The BUS_TS function uses semaphores to control access to specific
memory in a module located on the bus.
The BUS_TS function exchanges a Boolean TRUE (1) for the value
currently at the semaphore location. If that value was already a 1,
then the BUSTST function does not acquire the semaphore. If the
existing value was 0, the semaphore is set and the BUS_TS function
has the semaphore and the use of the memory area it controls. The
semaphore can be cleared and ownership relinquished by using the
BUSWRT function to write a 0 to the semaphore location. This
function locks the bus while performing the operation.
When the BUS_TS function receives power flow through its enable
input, the function exchanges a Boolean TRUE (1) with the address
specified by the RACK, SLOT, SUBSLOT, RGN, and OFF parameters.
The function sets the Q output on if the semaphore was available (0)
and was acquired. It passes power flow to the right whenever power
is received and no errors occur during execution.
Operands for BUS Test and Set
BUS_TS can be programmed as BUS_TS_BYTE or BUS_TS_WORD. For BUS_TS_WORD, the absolute
address of the module must be a multiple of 2. The absolute address is equal to the base address
plus the offset value.
Parameter Description
R
Rack number. UINT constant or variable.
S
Slot number. UINT constant or variable.
SS
Subslot number (defaults to 0). UINT constant or
variable.
RGN
Region (defaults to 1). WORD constant or
variable.
OFF
The offset in bytes. DWORD constant or variable. All except %S—%SC
ST
The status of the bus test and set operation.
WORD variable.
Q
Output set on if the semaphore was available (0).
Otherwise, Q is set off.
GFK-2950C
Chapter 4. Ladder Diagram (LD) Programming
Allowed Operands
All except %S—%SC
All except %S—%SC
All except %S—%SC
All except %S—%SC
All except variables located in %S—
%SC, and constant
Power flow
February 2018
Other
mnemonic:
BUS_TS_WORD
Optional
No
No
Yes
Yes
No
Yes
Yes
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