Z8F6421PM020SC Datasheet, PDF (64/299 Pages) Zilog, Inc. – High Performance 8-Bit Microcontrollers Z8 Encore-R 64K Series

Z8 Encore!^® 64K Series
Product Specification
44
System Reset
During a System Reset, the 64K Series devices are held in Reset for 66 cycles of the
Watch-Dog Timer oscillator followed by 16 cycles of the system clock. At the beginning
of Reset, all GPIO pins are configured as inputs.
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 0002H and 0003H and loads
that value into the Program Counter. Program execution begins at the Reset vector
address.
Reset Sources
Table 9 lists the reset sources as a function of the operating mode. The text following pro-
vides more detailed information on the individual Reset sources. A Power-On Reset/Volt-
age Brown-Out event always takes priority over all other possible reset sources to ensure a
full system reset occurs.
Table 9. Reset Sources and Resulting Reset Type
Operating Mode
Normal or HALT
modes
STOP mode
Reset Source
Reset Type
Power-On Reset / Voltage Brown-Out System Reset
Watch-Dog Timer time-out
when configured for Reset
System Reset
RESET pin assertion
System Reset
On-Chip Debugger initiated Reset
(OCDCTL[0] set to 1)
System Reset except the On-Chip Debugger is
unaffected by the reset
Power-On Reset / Voltage Brown-Out System Reset
RESET pin assertion
System Reset
DBG pin driven Low
System Reset
Power-On Reset
Each device in the 64K Series contains an internal Power-On Reset (POR) circuit. The
POR circuit monitors the supply voltage and holds the device in the Reset state until the
supply voltage reaches a safe operating level. After the supply voltage exceeds the POR
PS019915-1005
Reset and STOP Mode Recovery