This document describes the SIM (Set Interrupt Mask) instruction in microprocessors. The SIM instruction controls hardware interrupts by setting masking bits to enable or disable interrupts. It can also reset the RST7.5 flip-flop to ignore an RST7.5 interrupt without servicing it. Additionally, the SIM instruction allows for serial input/output of data by transferring bits from the instruction to output pins.

1. SIMINSTRUCTION
By
Ashish Mani

2. CONTENTS
 Introduction
 Format of SIM Instruction
 Explanation of Format of SIM
Instruction
CONTENTS:---

3. INTRODUCTION
 It is “Set Interrupt Mask” instruction.
 This instruction controls hardware interrupt of
microprocessor
 It is the type of Implicit Addressing mode and of Single Byte
instruction
It has three different function:---
a) To set masking bit for interrupt RST7.5 , RST6.5 and RST5.5
interrupts.
b) To reset RST7.5 flip-flop.
c) To implement serial input output

4. SIMINSTRUCTION
Harddware interrupt of
Micropressor Format of SIM instruction

5. EXPLANATIONOF SIMINSTRUCTION
1. a) If D6 = SDE (serial data enable) = 1 , the binary bit in D7 is transferred to
SOD (Serial output data) pin of microprocessor.
b) If D6 = 0, then A7 bit is not transferred to SOD pin
Hence data transfer is possible with SOD (serial output data) pin.
2. If D4 = 1, RST 7.5 is reset. This is used to ignore RST 7.5 without servicing it.
3. If D3= MSE (Masking Set Enable) = 1, then the binary bit in D2, D1 and D0 flip-flop
are transferred to masking flip-flop M7.5 , M6.5 , M5.5 flip-flop respectively.
a) If D3= MSE= 1 , A2= 0/1, then after SIM instruction, M7.5 will be 0/1.
Hence RST7.5 will be enabled/disabled respectively.
b) If D3= MSE= 0, then A2, A1, A0 are not transferred , value of M7.5,M6.5, M5.5
will be X ,X, X.