MC68306 Motorola, MC68306 Datasheet - Page 60

• Manufacturer Part Number: MC68306
• Description: Integrated EC000 Processor
• Manufacturer: Motorola

After the processor is reset, it reads the reset vector table entry (address $00000) and
loads the contents into the supervisor stack pointer (SSP). Next, the processor loads the
contents of address $00004 (vector table entry 1) into the program counter. Then the
processor initializes the interrupt level in the status register to a value of seven. No other
register is affected by the reset sequence. Figure 3-27 shows the timing of the reset
operation.
The active-low RESET signal is asserted by the EC000 core when a RESET instruction is
executed. This signal should reset all external devices (the EC000 core itself is not
affected). The processor drives RESET for 124 clock periods. The RESET signal is
asserted by an external source to reset the EC000 core. RESET by itself will reset the
EC000 core unless the processor is executing a RESET instruction. To guarantee a reset
of the core, RESET must be asserted for at least 132 clocks (i.e., longer than the
maximum duration of the RESET instruction), or RESET and HALT must be asserted
together for at least 10 clocks.
3.6 THE RELATIONSHIP OF
To properly control termination of a bus cycle for a retry or a bus error condition, DTACK,
BERR , and HALT should be asserted and negated on the rising edge of the processor
clock. This relationship assures that when two signals are asserted simultaneously, the
required setup time (specification #47, AC Electrical Specifications
Cycles) for both of them is met during the same bus state. External circuitry should be
designed to incorporate this precaution. A related specification, #48, can be ignored when
DTACK, BERR , and HALT are asserted and negated on the rising edge of the processor
clock.
3-28
BUS CYCLES
+ 5 VOLTS
NOTES:
RESET
1. Internal start-up time
2. SSP high read in here
3. SSP low read in here
HALT
V CC
CLK
Figure 3-27. Reset Operation Timing Diagram
4. PC High read in here
5. PC Low read in here
6. First instruction fetched here
T
T 4 CLOCKS
MC68306 USER'S MANUAL
100 MILLISECONDS
DTACK
,
BERR
All Control Signals Inactive.
Data Bus in Read Mode:
Bus State Unknown:
, AND
1
HALT
2
3
Ñ
Read and Write
4
MOTOROLA
5
6