Processor Control Instruction 8086 8086 Microprocessor by Ravinder Nath Rajotiya - December 14, 2020May 10, 20210 Share on Facebook Share Send email Mail Print Print Table of Contents Toggle Processor Control InstructionsFLAG CONTROLSExternal SynchronizationNO OPERATION Processor Control Instructions There are certain instructions in 8086 that control the processor flags, i.e. the flags can be set or reset by use of these instructions. Processor control instructions Description Comments/ example FLAG CONTROLS STC Set carry Flag ( CF=1) CLC Clear carry (CF=0) CMC Complement carry flag STD Set Direction flag, thus reverse traverSIng the string, i.e. SI or DI now point at the end of string, In each traverse SI/DI will be decremented Data segment Name db “MyString” Revrse_name db 8 dup(‘ ‘) Data ends Code segment Assume DS:data CS:code MOV AX, data MOV DS,AX CLD LEA SI,Name LEA DI, Reverse_name MOV CX, 08 REP MOVSB; Code ends CLD Clear Direction flag so that string traverse is from beginning, SI/DI will point to beginning of string STI Set interrupt enable flag to 1(enable interrupts) CLI DIsalee interrupts External Synchronization HLT HALT(do nothing) until interrupts WAIT Wait till SIgnal on TEST pin is low ESC Escape to external processor such as coprocessor LOCK Used as a prefix, to prevent another processor from taking bus while adjacent instruction executes. NO OPERATION NOP No action except fetch and decode. Share on Facebook Share Send email Mail Print Print