Rev 1.00

March 22, 2010

10

HT45B0K

SPI to USB Bridge

UCC Register

The UCC register is the system clock control register implemented to select the clock used by the

MCU. This register consists of USB clock control bit USBCKEN, second suspend mode control bit

SUSP2 and system clock selection bit SYSCLK. This register is also used to select which endpoint

FIFO is accessed by Endpoint FIFO Selection bits EPS2~EPS0. Further explanation on each of the

bits is given below:

UCC Register

Bit

7

6

5

4

3

2

1

0

Name

―

SYSCLK

―

SUSP2 USBCKEN

EPS2

EPS1

EPS0

R/W

―

R/W

―

R/W

R/W

R/W

R/W

R/W

POR

―

0

―

000

0

0

Bit 7

Unimplemented, read as “0”.

Bit 6

SYSCLK: System clock input selection

0: 12MHz clock is used

1: 6MHz clock is used

This bit is used to specify the system clock oscillator frequency used by the MCU. If

a 6MHz crystal oscillator or resonator is used, this bit should be set to 1. If a 12MHz

crystal oscillator or resonator is used, this bit should be set to 0.

Bit 5

Unimplemented, read as “0”.

Bit 4

SUSP2: Suspend mode 2 control

0: optimized setting in suspend mode

1: test setting in suspend mode. The band-gap circuit is turned off.

It is strongly recommended that this bit should be set to 0 when the USB interface is in

suspend mode. Otherwise, the unpredictable results will occur.

Bit 3

USBCKEN: USB clock enable control

0: USB clock is disabled

1: USB clock is enabled

When the USB device receives the suspend signal sent from the USB host, the USB

clock enable control bit USBCKEN should be set to 0 to reduce the power consumption.

Bit 2~0

EPS2~EPS0: Endpoint FIFO selection

000: Endpoint 0 FIFO is selected

001: Endpoint 1 FIFO is selected

010: Endpoint 2 FIFO is selected

011: Endpoint 3 FIFO is selected

100: Endpoint 4 FIFO is selected

101: Endpoint 5 FIFO is selected

11x: reserved for further expansion and can not be used.

The EPS2~EPS0 bits are used to select which endpoint is to be accessed. If the selected

endpoint does not exist, the related functions are not available.