Using C18 and a Timer to Interface PIC18 MCUs with UNI/O(TM) Bus-Compatible Serial EEPROMs

AN1191 Using C18 and a Timer to Interface PIC18 MCUs with UNI/O™ Bus-Compatible Serial EEPROMs The main features of 11XXX serial EEPROMs are: Author: Chris Parris * Single I/O pin used for communication Microchip Technology Inc. * EEPROM densities from 1 Kb to 16 Kb * Extremely small packages * Bus speed from 10 kHz up to 100 kHz INTRODUCTION * Wide 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- * Wide temperature range from -40°C to +125°C tion between devices. Microchip has addressed this * Over 1,000,000 erase/write cyclesneed by developing the UNI/O™ bus, a low-cost, easy- 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 with minimal effort.UNI/O bus-compatible serial EEPROMs can be used to enhance any application facing restrictions on avail- Figure 1 describes the hardware schematic for the able I/O. Such restrictions can potentially stem from interface between the Microchip 11XXX series of connectors, board space, or from the master device UNI/O bus-compatible serial EEPROMs and the itself. PIC18F25J10 microcontroller. The schematics show the connections necessary between theThe 11XXX family is the newest addition to Microchip microcontroller and the serial EEPROM as tested. TheTechnology's broad serial EEPROM product line, and software was written assuming these connections. Theis compatible with the newly developed UNI/O bus. single I/O connection between the microcontroller and the serial EEPROM includes a recommended pull-up resistor. FIGURE 1: CIRCUIT FOR PIC18F25J10 AND 11XXX SERIAL EEPROM PDIP MCLR 128RB7 272 RB6RA0 263 RB5RA1 254RA2 RB4 (2) VCC 245RA3 RB3 SOT-23 236V RB2DDCORE 5J10 227RA5 RB1 2 VCC (2) X VCC (1)X 218V RB0SS 20 k? 3VSS X 11 209 VOSC1 DD PIC18F2 1 SCIO