Datasheet PCF8574, PCF8574A (NXP) - 10

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NXP Semiconductors PCF8574; PCF8574A Remote 8-bit I/O expander for I2C-bus with interrupt 8.5 Interrupt output (INT)
The PCF8574/74A provides an open-drain output (INT) which can be fed to a corresponding input of the microcontroller (see Figure 10). As soon as a port input is changed, the INT will be active (LOW) and notify the microcontroller. An interrupt is generated at any rising or falling edge of the port inputs. After time tv(Q), the signal INT is valid. The interrupt will reset to HIGH when data on the port is changed to the original setting or data is read or written by the master. In the Write mode, the interrupt may be reset (HIGH) on the rising edge of the acknowledge bit of the address byte and also on the rising edge of the write to port pulse. The interrupt will always be reset (HIGH) on the falling edge of the write to port pulse (see Figure 8). The interrupt is reset (HIGH) in the Read mode on the rising edge of the read from port pulse (see Figure 9). During the interrupt reset, any I/O change close to the read or write pulse may not generate an interrupt, or the interrupt will have a very short pulse. After the interrupt is reset, any change in I/Os will be detected and transmitted as an INT. At power-on reset all ports are in Input mode and the initial state of the ports is HIGH, therefore, for any port pin that is pulled LOW or driven LOW by external source, the interrupt output will be active (output LOW). VDD device 1 device 2 device 16
PCF8574 PCF8574 PCF8574A
MICROCONTROLLER INT INT INT INT 002aad634
Fig 10. Application of multiple PCF8574/74As with interrupt
PCF8574_PCF8574A All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
Product data sheet Rev. 5 — 27 May 2013 10 of 33
Document Outline 1. General description 2. Features and benefits 3. Applications 4. Ordering information 4.1 Ordering options 5. Block diagram 6. Pinning information 6.1 Pinning 6.2 Pin description 7. Functional description 7.1 Device address 7.1.1 Address maps 8. I/O programming 8.1 Quasi-bidirectional I/Os 8.2 Writing to the port (Output mode) 8.3 Reading from a port (Input mode) 8.4 Power-on reset 8.5 Interrupt output (INT) 9. Characteristics of the I2C-bus 9.1 Bit transfer 9.1.1 START and STOP conditions 9.2 System configuration 9.3 Acknowledge 10. Application design-in information 10.1 Bidirectional I/O expander applications 10.2 How to read and write to I/O expander (example) 10.3 High current-drive load applications 10.4 Migration path 11. Limiting values 12. Thermal characteristics 13. Static characteristics 14. Dynamic characteristics 15. Package outline 16. Handling information 17. Soldering of SMD packages 17.1 Introduction to soldering 17.2 Wave and reflow soldering 17.3 Wave soldering 17.4 Reflow soldering 18. Soldering of through-hole mount packages 18.1 Introduction to soldering through-hole mount packages 18.2 Soldering by dipping or by solder wave 18.3 Manual soldering 18.4 Package related soldering information 19. Soldering: PCB footprints 20. Abbreviations 21. Revision history 22. Legal information 22.1 Data sheet status 22.2 Definitions 22.3 Disclaimers 22.4 Trademarks 23. Contact information 24. Contents