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MOTOROLA
MC68330 USER’S MANUAL
3- 45
3.7 RESET OPERATION
The MC68330 has reset control logic to determine the cause of reset, synchronize it if
necessary, and assert the appropriate reset lines. The reset control logic can
independently drive three different lines:
1. EXTRST (external reset) drives the external
RESET pin.
2. CLKRST (clock reset) resets the clock module.
3. INTRST (internal reset) goes to all other internal circuits.
Table 3-5 summarizes the result of each reset source. Synchronous reset sources are not
asserted until the end of the current bus cycle, whether or not
RMC is asserted. The
internal bus monitor is automatically enabled for synchronous resets; therefore if the
current bus cycle does not terminate normally, the bus monitor terminates it. Only single-
byte or word transfers are guaranteed valid for synchronous resets. Asynchronous reset
sources indicate a catastrophic failure, and the reset controller logic immediately resets
the system. Resetting the MC68330 causes any bus cycle in progress to terminate as if
DSACKx, or BERR had been asserted. In addition, the MC68330 appropriately initializes
registers for a reset exception.
Table 3-5 Reset Source Summary
Type
Source
Timing
Reset Lines Asserted by Controller
External
Synchronous
INTRST
CLKRST
EXTRST
Power-up
EBI
Asynchronous
INTRST
CLKRST
EXTRST
Software Watchdog
Sys Prot
Asynchronous
INTRST
CLKRST
EXTRST
Double Bus Fault
Sys Prot
Asynchronous
INTRST
CLKRST
EXTRST
Loss of Clock
Clock
Synchronous
INTRST
CLKRST
EXTRST
Reset Instruction
CPU32
Asynchronous
–
EXTRST
If an external device drives
RESET low, RESET should be asserted for at least 590 clock
periods to ensure that the MC68330 resets. The reset control logic holds reset asserted
internally until the external
RESET is released. When the reset control logic detects that
external
RESET is no longer being driven, it drives both internal and external reset low for
an additional 512 cycles to guarantee this length of reset to the entire system. Figure 3-27
shows the
RESET timing.
RESET
1 CLOCK
DRIVEN BY MC68
PULLED EXTERNALL
512 CLOCK
> 590 CLOCK