Z8F640x/Z8F480x/Z8F320x/Z8F240x/Z8F160x
Z8 Encore!®
26
System and Short Resets
During a System Reset, the Z8F640x family device is held in Reset for 514 cycles of the
Watch-Dog Timer oscillator followed by 16 cycles of the system clock (crystal oscillator).
A Short Reset differs from a System Reset only in the number of Watch-Dog Timer oscil-
lator cycles required to exit Reset. A Short Reset requires only 66 Watch-Dog Timer oscil-
lator cycles. Unless specifically stated otherwise, System Reset and Short Reset are
referred to collectively as Reset.
During Reset, the eZ8 CPU and on-chip peripherals are idle; however, the on-chip crystal
oscillator and Watch-Dog Timer oscillator continue to run. The system clock begins oper-
ating following the Watch-Dog Timer oscillator cycle count. The eZ8 CPU and on-chip
peripherals remain idle through the 16 cycles of the system clock.
Upon Reset, control registers within the Register File that have a defined Reset value are
loaded with their reset values. Other control registers (including the Stack Pointer, Regis-
ter Pointer, and Flags) and general-purpose RAM are undefined following Reset. The eZ8
CPU fetches the Reset vector at Program Memory addresses 0002Hand 0003Hand loads
that value into the Program Counter. Program execution begins at the Reset vector
address.
Reset Sources
Table 8 lists the reset sources and type of Reset as a function of the Z8F640x family
device operating mode. The text following provides more detailed information on the indi-
vidual Reset sources. Please note that Power-On Reset / Voltage Brown-Out events always
have priority over all other possible reset sources to insure a full system reset occurs.
Table 8. Reset Sources and Resulting Reset Type
Operating Mode
Reset Source
Reset Type
Normal or Halt modes Power-On Reset / Voltage Brown-Out System Reset
Watch-Dog Timer time-out
when configured for Reset
Short Reset
Short Reset
RESET pin assertion
On-Chip Debugger initiated Reset
(OCDCTL[1] set to 1)
System Reset except the On-Chip Debugger is
unaffected by the reset
Stop mode
Power-On Reset / Voltage Brown-Out System Reset
RESET pin assertion
DBG pin driven Low
System Reset
System Reset
PS017610-0404
Reset and Stop Mode Recovery
ZILOG [ ZILOG, INC. ]
