AT83C5136-RDTUL datasheet(30/171 Pages) ATMEL

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AT83C5134/35/36

7683B–USB–03/07

Stacked EEPROM

Overview

The AT83C5134/35/36 features a stacked 2-wire serial data EEPROM. The data

EEPROM allows to save from 512 Byte for AT24C04 version up to 32 Kbytes for

AT24C256 version. The EEPROM is internally connected to the microcontroller on SDA

and SCL pins.

Protocol

In order to access this memory, it is necessary to use software subroutines according to

the AT24Cxx datasheet. Nevertheless, because the internal pull-up resistors of the

AT83C5134/35/36 is quite high (around 100KΩ), the protocol should be slowed in order

to be sure that the SDA pin can rise to the high level before reading it.

Another solution to keep the access to the EEPROM in specification is to work with a

software pull-up.

Using a software pull-up, consists of forcing a low level at the output pin of the microcon-

troller before configuring it as an input (high level).

The C51 the ports are “quasi-bidirectional” ports. It means that the ports can be config-

ured as output low or as input high. In case a port is configured as an output low, it can

sink a current and all internal pull-ups are disconnected. In case a port is configured as

an input high, it is pulled up with a strong pull-up (a few hundreds Ohms resistor) for 2

clock periods. Then, if the port is externally connected to a low level, it is only kept high

with a weak pull up (around 100KΩ), and if not, the high level is latched high thanks to a

medium pull (around 10kΩ).

Thus, when the port is configured as an input, and when this input has been read at a

low level, there is a pull-up of around 100KΩ, which is quite high, to quickly load the

SDA capacitance. So in order to help the reading of a high level just after the reading of

a low level, it is possible to force a transition of the SDA port from an input state (1), to

an output low state (0), followed by a new transition from this output low state to input

state; In this case, the high pull-up has been replaced with a low pull-up which warran-

ties a good reading of the data.

AT83C5136-RDTUL データシート(PDF) 30 Page - ATMEL Corporation