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Machine Control Instructions (Part-I) - RIM and SIM

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RIM:
  • RIM stands for Read Interrupt Mask.
  • This instruction is used to copy the status of the interrupts into the accumulator.
  • This instruction is also used to read the serial data through the SID (Serial Input Data) pin.
  • No flags are affected.
  • It is a one byte instruction.
  • Implied addressing mode is used.
Example:
If after execution of RIM instruction, A = 0100 1011 = 4BH


It shows that RST 7.5 is pending, RST5.5 and RST 6.5 are masked, interrupt enable flip flop is set and SID is zero.

SIM:
  • SIM stands for Serial Interrupt Mask.
  • This instruction is used to mask the interrupts as desired.
  • The command byte which is used to mask the interrupts is loaded into the accumulator.
  • This instruction is also used to send the serial data through the SOD (Serial Output Data) pin.
  • No flags are affected.
  • It is a one byte instruction.
  • Implied addressing mode is used.
Example:
If we want to mask RST 7.5 and RST 6.5 and unmask RST 5.5, then accumulator should be loaded with 0EH i.e. A = 0000 1110 = 0EH.


It will also disable serial output data.
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