Cypress Semiconductor CY8C21534 Especificaciones descargar pdf (Pagina 42)

implemented to show outputs on the LCD. A separate SPI connection was programmed

into the Communications MCU and output to the temporary MCU which ran on 5 volts

and had an LCD. This way the whole system could stay at 3.3 volts and the responses

from the SD card could be forwarded and displayed for debugging.

Working with 3.3 volts resulted in problems in switching power to the individual areas

of the system. The transistors used for the switching of power were PNP BC556 [21] and

NPN BC546 [22] used in the Darlington setup to provide better current flow [23, 95].

The rated voltage is 5 volts on both. It was attempted to use these transistors with the

system’s 3.3 volts. The lower voltage did not allow for the proper current and the

switching was intermittent. To solve the problem, the 5 volts from the power supply

was taken into the collectors and switched using the MCUs 3.3 volts on the base. Then

the output was supplied to a MIC5200 voltage regulator [24] which dropped it to

3.3 volts for use in the system.

The largest issue of the project that presented itself was how to properly isolate the

two master SPI connections from each other and give alternate control over the SD

card. The use of the Darlington transistor setup was attempted on each data line but

that idea proved to supply too much stray capacitance and the signals were degraded

so that they would not work. Logic gates were attempted, such as the SN7408, and

the signal still seemed to be degraded beyond a usable amount. Several switching

integrated circuits and multiplexer integrated circuits were used including SN74LS243

transceiver, HCF4053, MM5616 multiplexer, and the HEF4066 quadruple bilateral

switch. All of them gave the same results. The issue was eventually resolved using the

HEF4066. It was found that the problem was a combination of issues. The first issue

being that Vcc on the integrated circuit needed to be 5 volts, though the enable, input,

and output could all be used with the 3 volt system. The second issue was that the

HEF4066 needed to be kept on while the enable pins were held low to effectively stop

a signal. The original method was to cut all power to the HEF4066 and assume that the

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Cypress Semiconductor CY8C21534 Especificaciones Pagina 42