BCM2835 データシートの表示（PDF） - Broadcom Corporation

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コンポーネント説明

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BCM2835

BCM2835 ARM Peripherals

Broadcom Corporation 

If the enable bits are clear you will have no access to a peripheral. You can not even read or

write the registers!

GPIO pins should be set up first the before enabling the UART. The UART core is build to

emulate 16550 behaviour. So when it is enabled any data at the inputs will immediately be

received . If the UART1_RX line is low (because the GPIO pins have not been set-up yet)

that will be seen as a start bit and the UART will start receiving 0x00-characters.

Valid stops bits are not required for the UART. (See also Implementation details). Hence

any bit status is acceptable as stop bit and is only used so there is clean timing start for the

next bit.

Looking after a reset: the baudrate will be zero and the system clock will be 250 MHz. So

only 2.5 µseconds suffice to fill the receive FIFO. The result will be that the FIFO is full and

overflowing in no time flat.

2.2 Mini UART

The mini UART is a secondary low throughput4 UART intended to be used as a console. It

needs to be enabled before it can be used. It is also recommended that the correct GPIO

function mode is selected before enabling the mini Uart.

The mini Uart has the following features:

• 7 or 8 bit operation.

• 1 start and 1 stop bit.

• No parities.

• Break generation.

• 8 symbols deep FIFOs for receive and transmit.

• SW controlled RTS, SW readable CTS.

• Auto flow control with programmable FIFO level.

• 16550 like registers.

• Baudrate derived from system clock.

This is a mini UART and it does NOT have the following capabilities:

• Break detection

• Framing errors detection.

• Parity bit

• Receive Time-out interrupt

• DCD, DSR, DTR or RI signals.

The implemented UART is not a 16650 compatible UART However as far as possible the

first 8 control and status registers are laid out like a 16550 UART. Al 16550 register bits

which are not supported can be written but will be ignored and read back as 0. All control

bits for simple UART receive/transmit operations are available.

4 The UART itself has no throughput limitations in fact it can run up to 32 Mega baud. But doing so requires

significant CPU involvement as it has shallow FIFOs and no DMA support.

06 February 2012 Broadcom Europe Ltd. 406 Science Park Milton Road Cambridge CB4 0WW

© 2012 Broadcom Corporation. All rights reserved

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