Applied Data Systems Bitsy Plus, Руководство пользователя

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Bitsy Plus User’s Manual
Page 26 ADS document # 110114-1001A
USB Host
The Bitsy Plus USB Host port allows you to connect one USB device to the Bitsy Plus. USB
mouse and keyboard are the most common client devices, but you can connect any USB function
device that has USB drivers installed on the Bitsy Plus.
Use a Type A connector for the host signals on J10 pins 14 and 16 (section 3.3.8). The mating
face of such a socket is shown at left. The USB standard also permits directly wiring the USB
signals to the target USB device (e.g. USB mouse). To connect more than one USB client device
to the Bitsy Plus, use a USB hub.
The USB protocol allows client devices to negotiate the power they need from 100 mA to 500 mA
in 100 mA increments. The Bitsy Plus supplies 5 V power through the USB_PWR pin. Make
sure to account for power used through USB in your Bitsy power budget (section 5.4.1). It is
recommended that you use a power switch.
The Bitsy Plus supports two power control signals on J10. USB_PWR_SENSE is an input that
detects over-current conditions. USB_PWR_CTRL an output that controls power to the USB
port. See the Bitsy Plus CF Personality Board (ADS p/n 170111-8000) for an example of how to
use these signals. Electrical specifications are in section 6.2.8.
USB Client
The Bitsy Plus includes a USB Client (or "Function") port. This interface allows the Bitsy Plus to
appear as a client device to USB Host devices such as desktop and laptop computers.
The USB Client signals are available on connector J3, pins 29 and 30. Connect these signals to a
USB client Type B socket (mating face shown at left). The USB standard also permits directly
wiring the USB signals to the host or to a host connector (e.g. USB mouse).
The Bitsy Plus supports the full USB connection speed (12 Mbit/s), so you must tie a 1.5 k
Ω
pull-
up to the USB+ signal to indicate this capability to host hardware.
USB_PWR is power supplied from the host computer. Since the Bitsy Plus is self-powered (not
powered by the USB cable), USB_PWR is not needed as a power input. However, USB_PWR is
useful for sensing when a USB cable is connected and for powering the 1.5k
Ω
pull-up resistor that
indicate to the host that the device supports 12Mbps. The Bitsy CF Personality Board reference
design (ADS p/n 170111-8000) for an example of such an application.
Revisions 5 and later of the Bitsy Plus add the USB_RECONN signal to J3, pin 33. This signal
interrupts power to the 1.5k
Ω
pull-up, simulating a cable disconnection to the USB host controller.
This signal can be used to force the host to re-enumerate the Bitsy Plus (e.g. after wakeup).
4.5.3 SPI Bus
Overview
The SPI Bus (Serial Peripheral Interface) is a full-duplex, synchronous serial protocol developed
by Motorola that can support multiple bus masters. The bus consists of a clock line, transmit and
receive lines, ground and one or more device selects. Each device on the bus requires its own
select line. A key feature of SPI is that data is clocked in both directions at the same time,
providing full-duplex data flow.
To clarify direction of the signals, the SPI bus master transmit line (STXD) is also known as
MOSI (Master Out, Slave In), while its receive line is known as MISO (Master In, Slave Out).
The Slave Select (SS) signal, which enables the slave device's transmitter, is also known as
SFRM2 on the Bitsy Plus.