Cypress Semiconductor CY8C21534 Especificações descarregar pdf (Página 28)

that the picture frame may access the file on the SD card. The picture is shown for a

specified amount of time after which the Control MCU will cut power to route 2

effectively turning off power to the enable read signal and electronic picture frame.

The process can be initiated at any time by the user by pressing one of the buttons.

The alternate enabling of the data lines is implemented due to the fact that both the

electronic picture frame and the Communications MCU are both master SPI units, and

they conflict with each other if connected simultaneously. The method that was found

to work the best to isolate which master was to use the SD card was the use of the

HEF4066 bilateral switch integrated circuit which can be seen in figure 15.

Figure 15: HEF4066 Bilateral Switch. Taken from HEF4066 Quadruple bilateral switch

Datasheet [15].

The HEF4066 bilateral switch consists of four logic switches as can be seen in the

figure. Each logic switch consists of an input, output, and an enable signal. For

this project two HEF4066 chips were used, one for the connection of the SD card to

the Communications MCU, and one for the connection of the SD card to the digital

photo frame. For writing purposes, the MCU is allowed to turn on its enable signal

giving it access to the SD card while the digital photo frame is held off. When the

writing is complete, the Communications MCU turns off its enable signal and loses

its power, effectively holding the enable signal to a logical 0 through a pull down

resistor. The Control MCU then gives power to the digital photo frame as well as its

enable signal allowing the photo frame to read the file. The switch requires 5 volts

to operate but can switch and be enabled with 3.3 volts making it an ideal choice

for the low voltage communications that are present in this project.

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Cypress Semiconductor CY8C21534 Especificações Página 28