Datasheet PCF8574, PCF8574A (NXP) - 6

NXP Semiconductors PCF8574; PCF8574A Remote 8-bit I/O expander for I2C-bus with interrupt Table 5. PCF8574A address map Pin connectivity Address of PCF8574A Address byte value 7-bit hexadecimal A2 A1 A0 A6 A5 A4 A3 A2 A1 A0 R/W Write Read address without R/W
VSS VSS VSS 0 1 1 1 0 0 0 - 70h 71h 38h VSS VSS VDD 0 1 1 1 0 0 1 - 72h 73h 39h VSS VDD VSS 0 1 1 1 0 1 0 - 74h 75h 3Ah VSS VDD VDD 0 1 1 1 0 1 1 - 76h 77h 3Bh VDD VSS VSS 0 1 1 1 1 0 0 - 78h 79h 3Ch VDD VSS VDD 0 1 1 1 1 0 1 - 7Ah 7Bh 3Dh VDD VDD VSS 0 1 1 1 1 1 0 - 7Ch 7Dh 3Eh VDD VDD VDD 0 1 1 1 1 1 1 - 7Eh 7Fh 3Fh
8. I/O programming 8.1 Quasi-bidirectional I/Os
A quasi-bidirectional I/O is an input or output port without using a direction control register. Whenever the master reads the register, the value returned to master depends on the actual voltage or status of the pin. At power on, all the ports are HIGH with a weak 100 A internal pull-up to VDD, but can be driven LOW by an internal transistor, or an external signal. The I/O ports are entirely independent of each other, but each I/O octal is controlled by the same read or write data byte. Advantages of the quasi-bidirectional I/O over totem pole I/O include:
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Better for driving LEDs since the p-channel (transistor to VDD) is small, which saves die size and therefore cost. LED drive only requires an internal transistor to ground, while the LED is connected to VDD through a current-limiting resistor. Totem pole I/O have both n-channel and p-channel transistors, which allow solid HIGH and LOW output levels without a pull-up resistor — good for logic levels.
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Simpler architecture — only a single register and the I/O can be both input and output at the same time. Totem pole I/O have a direction register that specifies the port pin direction and it is always in that configuration unless the direction is explicitly changed.
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Does not require a command byte. The simplicity of one register (no need for the pointer register or, technically, the command byte) is an advantage in some embedded systems where every byte counts because of memory or bandwidth limitations. 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 6 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