USB97C100 Standard Microsystems Corporation, USB97C100 Datasheet - Page 24

• Manufacturer Part Number: USB97C100
• Description: USB97C100 Multi-endpoint Usb Peripheral Controller(not Recommended For Designs)
• Manufacturer: Standard Microsystems Corporation

MCU Power Management Registers
Notes:
SMSC DS – USB97C100
The 8051 may program itself to run off of an internal Ring Oscillator having a frequency range between 4 and
12MHz. This is not a precise clock, but is meant to provide the 8051 with a clock source, without running the
24MHz crystal oscillator or the PLL
Switching between fast and slow clocks is recommended to save power.
Clock switching can be done on the fly as long as both clocks are running. When switching, it takes a total of six
clocks (3 clocks of the original clock plus 3 clocks of the switching clock) to guarantee the switching.
Time TBD is required from ROSC_EN=1 to MCUCLK_SRC=0.
[4:3]
[1:0]
BIT
7
6
5
2
(0x7F27 - RESET=0x40)
ISADMACLK_EXT
ISADMACLK[1:0]
MCUCLK_SRC
MCU_CLK[1:0]
ROSC_EN
CLOCK_SEL
SLEEP
NAME
Table 27 - MCU/ISADMA Clock Source Select
R/W
R/W
R/W
R/W
R/W
R/W
R/W
When PCON. 0 = 1 and SLEEP has been set to 1, the
ring oscillator will be gated off, then all oscillators will be
turned off for maximum power savings. (These two signals
can be used to generate nFCE)
0 = Ring Oscillator Disable.
1 = Ring Oscillator Enable. ROSC_EN must be set to 1
before the MCU can be switched to the internal Ring
Oscillator Clock source.
MCUCLK_SRC overrides MCUCLK_x clock select and
switches the MCU to the Ring Oscillator.
0 = Use Ring Oscillator. ROSC_EN must be enabled by
the MCU first.
1 = Use clock specified in MCU_CLK_[1:0]
[4:3] = 00: 8MHz
[4:3] = 01: 12MHz
[4:3] = 10: 16MHz
[4:3] = 11: 24MHz
Selects an external clock source for the 8237 ISADMA
controller for synchronizing the DMA with another block.
NOTE: This will initially be an external input, but may
eventually be used within the block to optimize
performance, or as some other internal clock source.
0 = Use ISADMACLK[1..0] select
1 = Use EXT_IN clock source for 8237
[1:0] = 00: Stopped
[1:0] = 01: 2MHz
[1:0] = 10: 4MHz
[1:0] = 11: 8MHz
Page 24
MCU/ISADMA CLOCK SOURCE SELECT
DESCRIPTION
Rev. 01/03/2001