Pending Interrupts or Read Interrupt Mask (RIM) instruction

Pending Interrupts or Read Interrupt Mask (RIM) instruction

Because there are several interrupt lines, when one interrupt request is being served other interrupt requests may occur and remain pending. The 8085 has an additional instruction called RIM (Read Interrupt Mask) to sense these pending interrupts. Read Interrupt Mask (RIM) – This instruction is used to read the status of the hardware interrupts (RST 7.5, RST 6.5, RST 5.5) by loading into the A register a byte which defines the condition of the mask bits for the interrupts. It also reads the condition of SID (Serial Input Data) bit on the microprocessor.

Instruction RIM:- Read Interrupt Mask. The is a 1-byte instruction that can be used for the following functions.

• To read interrupt masks. This instruction loads the accumulator with 8 bits indicating the current status of the interrupt masks.
• To identify pending interrupts. Bits D4, D5 and D6 identify the pending interrupts.
• To receive serial data. Bit D7 is used to receive serial data.

Figure: Interpretation of the Accumulator Bit Pattern for the RIM Instruction

Table: Interpretation of the Accumulator Bit Pattern for the RIM Instruction

Pin Number	Pin Name	Pin Details	Remark
D0	M 5.5	Interrupt Masks 5.5	0= Available/ Unmasked 1= Masked
D1	M 6.5	Interrupt Masks 6.5
D2	M 7.5	Interrupt Masks 7.5
D3	IE	Interrupt Enable Flag	If 0= Disable flip-flop. If 1= Enabled flip-flop.
D4	I 5.5	Pending Interrupt 5.5	If 0= No request Pending. If 1= Interrupt request Pending.
D5	I 6.5	Pending Interrupt 6.5
D6	I 7.5	Pending Interrupt 7.5
D7	SID	Serial Input Data bit	If any.

REFERENCES

1. R. S. Gaonkar, Microprocessor Architecture, Programming, and Applications with the 8085, Fifth Edition, Penram International Publishing (India) Private Limited.
2. S Ghoshal, Microprocessor Based System Design, Macmillan India Limited, 1996
3. M. Mano, Digital Logic and Computer Design, Prentice – Hall India
4. B. Ram - Fundamentals of Microprocessor and Microcontrollers
5. “Microprocessors: Principles and Applications” by A Pal
6. “Microprocessors and Microcontrollers : Architecture, Programming and Interfacing Using 8085, 8086 and 8051” by Soumitra Kumar Mandal
7. “Introduction to Microprocessors and Microcontrollers” by Crisp John Crisp
8. “Microprocessors And Microcontrollers” by A Nagoor Kani
9. “Microprocessors And Microcontrollers : Architecture, Programming and System Design 8085, 8086, 8051, 8096” by Krishna Kant
10. “8 - Bit Microprocessor” by Vibhute