I am working with 8 YS-17 flame sensors and may need more in the future. There are only two INT0 and INT1 in port 3. Is there any way to get the other interrupts or I/Os to work as external interrupts?

The microcontroller is an AT89S52 and the oscillator is running at 16MHz.

  • 2
    \$\begingroup\$ It was common practice to use a single interrupt pin for multiple interrupts in small microprocessors and microcontrollers and let the interrupt handler work out which device caused the interrupt. \$\endgroup\$ Commented Jan 3, 2021 at 15:02
  • \$\begingroup\$ but how to use a single interrupt pin for multiple interrupts ? @PeterSmith \$\endgroup\$ Commented Jan 3, 2021 at 15:12
  • 1
    \$\begingroup\$ Why on earth you even need an interrupt at all? Does it matter if you detect flames with 1 microsecond or 1 second accuracy? \$\endgroup\$
    – Justme
    Commented Jan 3, 2021 at 15:50

1 Answer 1


One option is to use an I/O expander such as the MCP23017 or MCP23S17 (I²C or SPI). These chips can record an interrupt on any of 16 pins and report it over a single (additional) pin. Reading two 8-bit registers will tell you which of the 16 pins sent the interrupt. This chip is also available in an 8-port version (MCP23008 or MCP23S08).

  • \$\begingroup\$ MCP23017 or MCP23S17 don't exist in the ICs markets \$\endgroup\$ Commented Jan 3, 2021 at 15:22
  • \$\begingroup\$ @KiroloesAmir Check here, for example. \$\endgroup\$ Commented Jan 3, 2021 at 15:23
  • \$\begingroup\$ @AlexHajnal the link you suggest gives "0 results". Perhaps the parts are available in some countries, not in others? \$\endgroup\$ Commented Jan 3, 2021 at 16:03
  • \$\begingroup\$ @MathKeepsMeBusy Perhaps. Normally their site will optionally redirect to a local branch if you're not in the US. Given that Mouser is a US company it's prohibited from doing business with some countries (Iran, North Korea, etc.) by ITAR so might return no results for that country. Just conjecture on my part; the search gives the same results on a number of their sites (USA, France, Thailand, India, Estonia, Turkey, China). \$\endgroup\$ Commented Jan 3, 2021 at 16:10

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