Interrupts with the 8031

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Interrupts with the 8031
ECET3220
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Types of Interrupts

• Externally triggered (EX0,EX1)
• Timing/Counter INTs (T1,T0)
• Serial Port INTs (ES)
• Recall
• Interrupts cause normal program
• operation to halt and places the
• return address of the next
• instruction (PC) on the stack.

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Vector Addresses

• The PC is set to the proper address value when
  an interrupt is received
• Reset all to default states (POR) 00H
• External INT0 (IE0) 03H
• Counter/Timer 0 (TF0) 0BH
• External INT1 (IE1) 13H
• Counter/Timer 1(TF1) 1BH
• Serial Interrupt (RITI) 23H

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8031 Pins of Interrupts

• RI is P3.0
• TI is P3.1
• INT0 is P3.2
• INT1 is P3.3
• T0 is P3.4
• T1 is P3.5
• Remember to write a 1 to these Port bits if
  they are used as inputs.

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Enabling Interrupts

• In order to enable interrupts, use
• the IE control byte. (bit addressable)
• EA1 Interrupts are enabled individually
• EA0 means no interrupts acknowledged
• EX11 means to enable external INT 1
• EX10 means to disable external INT 1
• ES,ET0,ET1,EX0 - work in a similar
• manner as EX1 to enable or disable

EA --- --- ES ET1 EX1 ET0 EX0
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Interrupt Priority

• To change interrupt priority, use the IP byte.
  (bit addressable)
• If the bit is 0, the corresponding interrupt has
  a lower priority and if the bit is 1 the
  corresponding interrupt has a higher priority.
  (Example 00001010 changes the priority order from
  the default order to TF0, TF1, IE0, IE1, RI or
  TI.

--- --- --- PS PT1 PX1 PT0 PX0
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Interrupt Control Registers

• TCON (bit addressable)

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0

• TMOD (NOT bit addressable)

GATE C/T M1 M0 GATE C/T M1 M0

• SCON (bit addressable)

SM0 SM1 SM2 REN TB8 RB8 TI RI
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