DS80C320-MCG Datasheet, PDF (96/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
CRYSTAL RESUME FROM STOP MODE
If the microcontroller does not contain a ring oscillator, or if the RGSL bit is 0, a device exiting Stop
mode must restart operation using the external crystal as a clock source. The device will experience a
power-on reset delay of 65536 external clock cycles to allow the crystal to begin oscillation and the
frequency to stabilize. Once this delay is complete, software will begin execution from either address
0000h or the appropriate interrupt vector, depending on the stimulus to exit Stop mode. The same 65536
external clock cycle delay is performed if an external crystal oscillator is used instead of an external
crystal.
PIN STATES IN POWER SAVING MODES Table 7-1
DEVICE
MODE
ALE PSEN P0 (AD0–7)
P1
DS80C310
Idle or Stop
1
1
Latched¹
Port data²
DS80C320
All Others
Internal program
execution
All Others
Idle or
1
1
Port data²
Port data²
Stop
Idle
1
1
Latched¹
Port data²
External program
execution
All Others
Stop
1
1
Port data ²
Port data²
External program
execution
P2
Latched³
Port data²
Latched³
Port data⁴
P3
Port data²
Port data²
Port data²
Port data²
1_{Port exhibits opcode following instruction that sets the Stop bit. Port 0 is operating in true bi-directional}
mode, and will drive both a logic 1 and a logic 0.
2_{Port reflects data stored in corresponding Port SFR. Port 0 functions as an open-drain output in this}
mode.
3_{Port exhibits address MSB of opcode following instruction that sets the Stop bit.}
4_{Port reflects data stored in corresponding Port SFR. In this mode, the port uses weak pull-ups. If a bit in}
the P2 SFR is a 1, the corresponding device pin will transition slowly to a high when the reset state is
entered.
RING OSCILLATOR WAKE UP FROM STOP
A typical low power application is to keep the processor in Stop mode most of the time. Periodically, the
system will wake up (using an external interrupt), take a reading of some condition, then return to sleep.
The duration of full power operation is as short as possible. One disadvantage to this method is that the
clock must be restarted prior to performing a meaningful operation. This start-up period is a waste of
time and power since no work can be performed. The High-Speed Microcontroller provides an
alternative.
If the Ring Select (RGSL) is enabled, the High-Speed Microcontroller can exit Stop mode running from
an internal Ring Oscillator. Upon receipt of an interrupt, this oscillator can start instantaneously,
allowing software execution to begin immediately while the oscillator is stabilizing. Once 65,536 clock
cycles have been detected, the CPU will automatically switch to the normal oscillator as its clock source.
Some devices incorporate the option of continuing to run from the ring oscillator following Stop mode
even after the 65,536 clock cycle period. However, if the required interrupt response is very short, the
software can re-enter Stop mode before the crystal is even stable. In this case, Stop mode can be invoked
and both oscillators will be stopped.
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