The 8-bit I/O chip “Type PCF8574 is very popular: it is used, among others, on the AD-DA 1/0 module, the opto relay card, and the LC display – all published within the past 12 months (see References). Since it is often desirable to connect a number of 8574 modules to the 12C bus, it is possible to give each IC a different address via inputs AO-A2. As therefore only eight addresses can be set, it might be expected that this is also the maximum number of ICs that can be connected to the bus. It is, however, possible to connect 16 PCF8574s, because there are two variants of the IC, each with a different address. The standard PCF8574 has, as is well known, the basic address 40HEx• The variant, the PCF8574A, has the basic address70HEx• Otherwise the two types are identical and, therefore, completely interchangeable. Thus, eight standard and eight variant types of the IC can be connected to one bus.
1. 12C interface for PCs. Elektor Electronics
2. ADC/DAC and I/O for 12C bus. Elektor
Electronics March 1992
3. I2C LED display. Elektor Electronics
4. 12C opto/relay card. Elektor Electronics