User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 3: System Overview
Page
27
summarizes the reset options.
During reset pull-up and pull-down resistors on the generic Address/Data bus are used to set static system
options. These pins have weak internal pull-up or pull-down resistors (as described in the Hardware Data
Sheet), external resistors are required to set the other state. These options change the behavior of pins that
need to be active at startup time to ensure proper operation.
Table 7: Operation of Different Reset Sources
COLDRES_L
pin asserted
Software
System Reset
system_cfg[60]
Watchdog
2nd time-out
Type=system
RESET_L
pin
asserted
Software
Soft Reset
system_cfg[58]
Watchdog
2nd Time-
out
Type=sbsoft
Sample pll_div bits
Restart PLL
Clear system_cfg[63]
Y
-
-
-
-
-
Sample configuration
bits (other than pll_div)
Y
Y
-
-
-
-
Assert RESETOUT_L
Y
Y
Y
Y
-
-
Reset ZBbus
Y
Y
Y
Y
Y
Y
Reset Agents
Y
Y
Y
Y
Y
Y
Table 8: Static Configuration Options
IO_AD
Bit
Name
Pulled Up to 3.3V
Pulled Down
Section
0
Reserved
Reserved
Normal Operation.
N/A
1
clk100_src
The internal 100MHz clock and
IO_CLK100 come directly from
the CLK100_p reference. The
IO_CLK100 will have a duty
cycle only a little worse than the
reference clock.
The internal 100MHz clock
and IO_CLK100 are
generated by dividing down
the output of the PLL that
feeds the CPU clock. The
IO_CLK100 will match the
internal clocking and will run
at a few MHz (typically less
than 10MHz) during
COLDRES_L.
2
ldt_minrstcnt
Broadcom Use Only.
Enable HyperTransport reset
test mode.
Normal Operation.
N/A
3
ldt_bypass_pll
Broadcom Use Only.
Bypass the HyperTransport PLL.
Normal Operation.
N/A
4
pci_test_mode
Broadcom Use Only.
Enable PCI test mode.
Normal Operation.
N/A
5
iob0_div
IOB0 clock is CPU clock/3
Use with slow CPU clocks.
IOB0 clock is CPU clock/4
Use with fast CPU clocks.
6
iob1_div
IOB1 clock is CPU clock/2
Use with slow CPU clocks.
IOB1 clock is CPU clock/3
Use with fast CPU clocks.
11:7
pll_div
These bits are used to set the PLL clock ratios