DS80C400 Maxim, DS80C400 Datasheet - Page 94

• Manufacturer Part Number: DS80C400
• Description: The DS80C400 network microcontroller offers the highest integration available in an 8051 device
• Manufacturer: Maxim

External Reset Pins
The DS80C400 has both reset input (RST) and reset output (RSTOL) pins. The RSTOL pin supplies an active-low
reset output when the microcontroller is reset through a high on the RST pin, a timeout of the watchdog timer, a
crystal oscillator fail, or an internally detected power-fail. The timing of the RSTOL pin is dependent on the source
of the reset.
Note: When connecting the DS80C400 to an external PHY, do not connect the
Doing so may disable the Ethernet transmit.
Idle Mode
Setting the IDLE bit (PCON.0) invokes the idle mode. Idle leaves internal clocks, serial ports, and timers running.
Power consumption drops because memory is not being accessed and instructions are not being executed. Since
clocks are running, the idle power consumption is a function of crystal frequency. The CPU can exit idle mode with
any interrupt or a reset. Because PMM consumes less power than idle mode, and leaves the timers and CPU
operating, idle mode is no longer recommended for new designs, and is included for backward-software
compatibility only.
Stop Mode
Setting the STOP bit of the power-control register (PCON.1) invokes stop mode. Stop mode is the lowest power
state (besides power off) since it turns off all internal clocking. All microcontroller operation ceases at the end of the
instruction that sets the STOP bit. The CPU invokes stop mode only when the CAN controller has been disabled
(through the SWINT or CRST bits in the C0C SFR) and when the Ethernet controller has been placed in sleep
mode. The CPU can exit stop mode through an external interrupt, Ethernet power-mode interrupt, CAN interrupt, or
a reset condition. Internally generated interrupts (timer, serial port, watchdog) cannot cause an exit from stop mode
because internal clocks are not active in stop mode. See the DC Electrical Specifications section for I
maximum stop mode currents.
Bandgap Select
The DS80C400 provides two enhancements to stop mode. As described below, the device provides a bandgap
reference to determine power-fail interrupt and reset thresholds. The bandgap reference is controlled by the
bandgap select bit, BGS (EXIF.0). Setting BGS to a 1 keeps the bandgap reference enabled during stop mode.
The default or reset condition of the bit is logic 0, which disables the bandgap during stop mode. This bit does not
enable/disable the internal reference during full power, PMM, or idle modes.
With the bandgap reference enabled, the power-fail reset and power-fail interrupt sources are valid means for
leaving stop mode. This allows software to detect and compensate for a power supply sag or brownout, even when
in stop mode. When BGS = 1, the internal bandgap and associated comparator circuitry consume a small amount
of additional current during stop mode. If a user does not require a power-fail reset or interrupt while in stop mode,
the bandgap can remain disabled. Only the most power-sensitive applications should disable the bandgap
reference in stop mode, as this results in an uncontrolled power-down condition.
Ring Oscillator
The second enhancement to stop mode reduces power consumption and allows the device to restart instantly
when exiting stop mode. The ring oscillator is an internal clock that can optionally provide the clock source to the
microcontroller when exiting stop mode in response to an interrupt.
During stop mode the crystal oscillator is halted to maximize power savings. Typically 1ms to 7ms are required for
an external crystal to begin oscillating again once the device receives the exit stimulus. The ring oscillator, by
contrast, is a free-running digital oscillator that has no startup delay. The ring oscillator feature is enabled by setting
the ring oscillator select bit, RGSL (EXIF.1). If enabled, the microcontroller uses the ring oscillator as the clock
Power-On Reset
External Reset
Power-Fail
Watchdog Timer Reset
Oscillator-Fail Detect
RESET TYPE/SOURCE
65,536 t
< 1.25 machine cycles
65,536 t
Two machine cycles
65,536 t
CLK
CLK
CLK
(as described in Power Cycle Timing Characteristics)
(as described in Power Cycle Timing Characteristics)
(as described in Power Cycle Timing Characteristics)
RSTOL DURATION
94 of 97
RSTOL
to the reset of the PHY.
CC1
and I
CC3