8051 Flash Microcontroller

Application Note

0628DMICRO6/11Interfacing AT25XXX Serial EEPROMs with Atmel AT89LP Microcontrollers

Features Example Read/Write Routines for Accessing Atmel AT25XXX Serial EEPROMs Assembly Source Provided Applicable to any AT89LP Microcontroller

1. Serial Peripheral InterfaceSerial memory devices offer significant advantages over parallel devices in applica-tions where lower data transfer rates are acceptable. In addition to requiring lessboard space, serial devices allow microcontroller I/O pins to be conserved. This isespecially valuable when adding external memory to low pin count microcontrollerssuch as the Atmel AT89LP2051 and AT89LP4052.

This application note presents a suite of software routines which may be incorporatedinto a users application to allow AT89LP microcontrollers to read from and write toAT25XXX serial EEPROMs. All six AT25XXX device operations are supported: readmemory, write memory, read status, write status, (set write protection levels), writeenable and write disable. Routines are also provided to read from and write to mem-ory utilizing the page mode of the AT25XXX. The software supports both 3-wire and 4-wire configurations and meets all AT25XXX family timing requirements when run onan AT89LP microcontroller with a 12 MHz clock.

2. HardwareThe AT25XXX may be connected to the AT89LP microcontroller in either a 3-wire(Figure 3-1) or 4-wire (Figure 3-2) configuration. In the 3-wire configuration, theEEPROM serial data in (SI) and serial data out (SO) pins are both connected to thesame microcontroller I/O pin, thereby saving a pin. This is possible because the micro-controller I/O pins can be dynamically reprogrammed as input or output.

3. SoftwareSoftware for this application note may be downloaded from the Atmel Web Site. Con-sult the comment block at the beginning of the source code file for detailed informationon features and operation.

Figure 3-1. 3-Wire Configuration

Figure 3-2. 4-Wire Configuration

AT89LP2052

AT89LP205220628DMICRO6/11

Interfacing with AT25XXX EEPROMs

0628DMICRO6/11

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Features1. Serial Peripheral Interface2. Hardware3. Software