B&B Electronics Parallel Printer Card PIOC Manual de usuario descargar pdf (Pagina 13)

GHI Electronics,LLC USBwiz User Manual

Communication Interface selection

4. Communication Interface selection

4.1. Selecting an Interface

USBwiz uses UART, SPI or I2C to communicate with any external microcontroller. At

power up, USBwiz samples MODE0 and MODE1 to determine what interface to use. The

MODE pins have a built in pull up resistors to default the pin to 1. Do not connect these

pins to VCC, leave unconnected for 1 or connect to GND for 0.

MODE0 MODE1 Interface

0 0 Force boot loader. *

1 0 I2C

0 1 UART

1 1 SPI

* In this mode the boot loader will not execute the firmware and will run UART at 9600 baud.

4.2. UART Interface

In UART mode, UART_TX pin is used to send data/responses to your microcontroller and

UART_RX pin to receive commands/data from your microcontroller. The default baud rate

for UART is 9600 baud, 8-bit, no parity and 1 stop bit. USBwiz can be set to different baud

rates.

CTS and RTS lines must be used in high band width applications. CTS pin is an input to

USBwiz. When it is high USBwiz will not send data and will wait for CTS to go low. CTS

should be low as long as possible to not slow down USBwiz. RTS pin is an output from

USBwiz and it is set high when USBwiz FIFO is near full. Depending on data transfer

speed, RTS pin may never go high because USBwiz is contentiously emptying the FIFO.

Note: The internal UART has hardware TX FIFO that is 16 byte long. After asserting CTS,

USBwiz may still send the internal FIFO, up to 16 bytes.

Important: USBwiz will NOT send any data if CTS pin is high! If this pin is not used then it

must be connected to ground.

4.3. SPI Interface Mode

In SPI mode six pins are used for communication to implement slave SPI, including two

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B&B Electronics Parallel Printer Card PIOC Manual de usuario Pagina 13