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instructions:bre [2018/03/10 15:49] (current)
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 +===== Branch Reinstate (BRE)/OP=90 =====
 +
 +==== Format ====
 +
 +^  OP  ^  AF  ^  BF  ^
 +
 +''OP = 90''
 +
 +**AF** The A Variant which determines the state in which the processor is to operate subsequent to the execution of the instruction.  If the most significant digit of AF is equal to zero, the reinstated program is in //Normal State// and is responsive to interrupts.   If not equal to zero, the reinstated program is in non-interruptable //Control State//.  If the least significant digit of AV is not equal to zero, the trace toggle is set, which causes a branch communicate at the end of the next instruction.  Indirect field length can be specified.
 +
 +**BF** The B Variant is unused and ignored.  Indirect field length can be specified.
 +
 +^ Note | This is a privileged instruction.  The base must equal zero.  |
 +^ Note | This instruction is obsolete.  |
 +
 +==== Function ====
 +
 +The BRE instruction branches from a control program in order to reinstate
 +another program, either in //Control// or //Normal// state.  In reinstating
 +the program, the BRE reads the following information from reserved memory
 +addresses 61 through 76, and places in the appropriate registers and
 +flip/flops.  Typical this instruction restores the processor to the state that
 +existed when a Branch Communicate instruction was executed.  The Next Program
 +Instruction Address, the Base, the  Limit, the
 +[[processor_state::overflow_flag | Overflow Toggle]] and
 +[[processor_state::comparison_flags | Comparison]]
 +Toggles are restored as indicated by the contents of memory address 61 through
 +76 (refer to [[instructions:bct_pre_omega|BCT (Pre-Omega)]]).
 +
 +If the interrupt toggle is set at the beginning of this instruction and
 +the AF is equal to zero, a [[instructions:bct_pre_omega|BCT (Pre-Omega)]] to
 +memory address 94 is executed, and the contents of memory address 61 through
 +76 remains unchanged.
 +
 +==== Comparison Flags ====
 +
 +The comparison flags are restored from memory.
 +
 +==== Overflow Flag ====
 +
 +The overflow flag is restored from memory.
  
instructions/bre.txt ยท Last modified: 2018/03/10 15:49 (external edit)
 
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