Svc_Req 56: Logic Driven Read Of Nonvolatile Storage; Discrete Memory; Storage Disabled Conditions; Maximum Of One Active Instruction - GE PACSystems RX7i Cpu Programmer's Reference Manual

6.32 SVC_REQ 56: Logic Driven Read of Nonvolatile Storage

PACSystems controllers support a 64KB nonvolatile flash memory area, which can be accessed by
the logic-driven read/write service requests. Values are stored in the nonvolatile storage area using
SVC_REQ 57: Logic Driven Write to Nonvolatile Storage. These values are applied to the controller
user memory on power-up.
If you want only to write to nonvolatile storage and have the values restored on a power cycle, you
may not need to use SVC_REQ 56. However, a logic driven read from nonvolatile storage can be
commanded as needed. For example, you can use #FST_SCN with SVC_REQ 56 calls to force a reload
on each STOP Mode to RUN Mode transition.
SVC_REQ 56 specifies a read operation from nonvolatile storage when the PACSystems is running.
You can specify which reference address range to read and optionally a different destination
memory location in CPU memory in which to place the read data. Using different memory locations
enables you to set up a comparison between existing values in CPU memory with values in
nonvolatile storage.
SVC_REQ 56 execution time will vary depending on the number of values stored in nonvolatile
storage, as it will find the most recent value for the requested reference address range.
You can read up to 32 words (64 bytes) inclusively per invocation of SVC_REQ 56.
6.32.1

Discrete Memory

Discrete memory can be read as individual bits or as bytes. For more information, refer to Memory
Type Codes below.
If a discrete memory destination is forced, the forced value remains intact in CPU memory even
though the count in word 10 (address + 10) indicates that all the data was read and transferred.
If a memory location has an associated transition bit and SVC_REQ 56 causes a transition on that
value, the transition bit is set.
6.32.2

Storage Disabled Conditions

By default, the following write operations disable SVC_REQ 56 until logic is written to nonvolatile
storage:
▪ RUN Mode Store (RMS), even if a second RMS reverts everything to the original state.
▪ Test-Edit session, even when you cancel your edits.
▪ Word-for-word change.
▪ Downloading to RAM only of a stopped PACSystems CPU, even if the downloaded contents are
equal to the contents already on the nonvolatile storage. Setting bit 0 of input word 8 (address +
7) to a value of 1 enables SVC_REQ 56 despite the above conditions.
6.32.3

Maximum of One Active Instruction

When SVC_REQ 56 is active, it does not support an interrupt that attempts to activate SVC_REQ 57
or a second instance of SVC_REQ 56. If an attempt fails, an error indicating that another instance is
active will be returned.
6.32.4

ENO and Power Flow To The Right

If the status is Success or Partial Read (see address+9), on the SVC_REQ instruction, ENO is set to
True in FBD and ST, and power flow passes to the right in LD.
GFK-2950C
Chapter 6. Service Request Function
February 2018 331