AT83C5136 Atmel Corporation, AT83C5136 Datasheet - Page 29

• Manufacturer Part Number: AT83C5136
• Manufacturer: Atmel Corporation

Specifications of AT83C5136

• Max. Operating Frequency: 32 MHz
• Cpu: 8051-12C
• Max I/o Pins: 34
• Usb Transceiver: 1
• Usb Speed: Full Speed
• Usb Interface: Device
• Spi: 1
• Twi (i2c): 1
• Uart: 1
• Sram (kbytes): 1.25
• Eeprom (bytes): 512
• Operating Voltage (vcc): 2.7 to 3.6
• Timers: 4
• Mask Rom (kbytes): 32
• Watchdog: Yes

10. Stacked EEPROM
10.1
10.2
7683C–USB–11/07
Overview
Protocol
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.
In order to access this memory, it is necessary to use software subroutines according to the
AT 24Cx x da tashee t. Never thele ss , beca use the in te rnal pul l-u p re sis tors 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 microcontroller
before configuring it as an input (high level).
The C51 the ports are “quasi-bidirectional” ports. It means that the ports can be configured 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 warranties a good reading of the data.
AT83C5134/35/36
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