AN1184 Using a Timer to Interface 8051 MCUs with UNI/O™ Bus-Compatible Serial EEPROMs The main features of 11XXX serial EEPROMs are: Author: Alexandru Valeanu • Single I/O pin used for communication Microchip Technology Inc. • EEPROM densities from 1 Kbits to 16 Kbits • Extremely small packages INTRODUCTION • Bus speed from 10 kHz up to 100 kHz • Voltage range from 1.8V to 5.5V As embedded systems become smaller, a growing • Low-power operation need exists to minimize I/O pin usage for communica- tion between devices. Microchip has addressed this • Temperature range from -40°C to +125°C need by developing the UNI/O™ bus, a low-cost, easy- • Over 1,000,000 erase/write cycles to-implement solution requiring only a single I/O pin for This application note is part of a series that provide bidirectional communication. source code to help the user implement the protocol UNI/O bus-compatible serial EEPROMs can be used to with minimal effort. enhance any application facing restrictions on avail- Figure 1 describes the hardware schematic for the in- able I/O. Such restrictions can potentially stem from terface between the Microchip 11XXX series of UNI/O connectors, board space or from the microcontroller bus-compatible serial EEPROMs and NXP’s itself. P89LPC952 8051-based MCU. The schematic shows The 11XXX family is the newest addition to Microchip the connections necessary between the MCU and the Technology’s broad serial EEPROM product line, and serial EEPROM as tested. The software was written is compatible with the newly developed UNI/O bus. assuming these connections. The single I/O connec- tion between the MCU and the serial EEPROM in- cludes a recommended pull-up resistor. A decoupling CC and VSS is also recommended.capacitor across V FIGURE 1: CIRCUIT FOR P89LPC952 MCU AND 11XXX SERIAL EEPROM (1) VCC 11XXX 2 VCC (2) 3 10 k?SSV 7P1.3 INT0/SDA1 SCIO P89LPC952