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2-1
Hardware Overview
Hardware Overview
The USB keyboard/hub EVM features the TUSB2136 and the TPS2149 made
by Texas Instruments. The EVM is a two-board set made up of a stand alone
two-port hub (edge #6436539) and a miniature QWERTY keyboard (edge
#6436540). Jumpers (0-Ω resistors) and jumper blocks provided on the EVM
are installed with the factory settings. The settings are described in Table 3–2.
Review all setting changes prior to powering the EVM. Improper settings could
result in damage to some of the EVM components. The factory settings allow
the EVM to operate using a 12-MHz crystal along with an I
2
C EEPROM. The
EVM has also been configured to work only in bus-powered mode. The
firmware installed at the factory and stored in the EEPROM allows the EVM
to function as a two port keyboard hub. Users are responsible for developing
their own application firmware for the target hardware device.
The EVM uses a TUSB2136, USB keyboard/hub controller, made by Texas
Instruments, to communicate with the host and the downstream devices. A
USB cable is needed to connect the root hub of the PC to the EVM type B
connector (J5). The downstream devices connect to the EVM via the J6 and
J7 connectors. These downstream devices are powered through the
TPS2149, a power management device that integrates an LDO and two power
switches into one small package. The LDO is used to provide power to the
TUSB2136. The USB specification requires that downstream ports remain off
until enumeration is complete. Together, the TUSB2136 and the TPS2149
ensure the hub meets this requirement. Two other connectors, J3 and J4,
allow easy connection to the TUSB2136 general-purpose I/O lines. These
lines are used to implement the keyboard function. The miniature QWERTY
keyboard plugs directly into J3 and J4 to implement a fully functional keyboard.
Jumpers, test points, and LEDs have been added for testing, troubleshooting
and debugging purposes. There are test points on the differential pair lines of
the upstream B-type connector and the two downstream A-type connectors.
The I
2
C port can be probed directly on the EEPROM. Six LEDs are provided
for quick feedback during firmware debugging or as status information. One
LED (D1) is fixed to provide power and suspend status of the TUSB2136
device. An RS–232 port is available for monitoring 8052 MCU activity. The port
uses a one-to-one cable and not a null-modem cable.
Chapter 2