MC68HC000RC8 Freescale Semiconductor, MC68HC000RC8 Datasheet - Page 103

• Manufacturer Part Number: MC68HC000RC8
• Description: IC MPU 32BIT 8MHZ 68-PGA
• Manufacturer: Freescale Semiconductor

Specifications of MC68HC000RC8

• Processor Type: M680x0 32-Bit
• Speed: 8MHz
• Voltage: 3.3V, 5V
• Mounting Type: Surface Mount
• Package / Case: 68-PGA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -

The value of the saved program counter does not necessarily point to the instruction that
was executing when the bus error occurred, but may be advanced by as many as five
words. This incrementing is caused by the prefetch mechanism on the MC68010 that
always fetches a new instruction word as each previously fetched instruction word is used.
However, enough information is placed on the stack for the bus error exception handler to
determine why the bus fault occurred. This additional information includes the address
being accessed, the function codes for the access, whether it was a read or a write
access, and the internal register included in the transfer. The fault address can be used by
an operating system to determine what virtual memory location is needed so that the
requested data can be brought into physical memory. The RTE instruction is used to
reload the internal state of the processor at the time of the fault. The faulted bus cycle is
then rerun, and the suspended instruction is completed. If the faulted bus cycle is a read-
modify-write, the entire cycle is rerun, whether the fault occurred during the read or the
write operation.
An alternate method of handling a bus error is to complete the faulted access in software.
Using this method requires the special status word, the instruction input buffer, the data
input buffer, and the data output buffer image. The format of the special status word is
6-18
Figure 6-8. Exception Stack Order (Bus and Address Error)
SP
NOTE: The stack pointer is decremented by 29 words, although only 26
M68000 8-/16-/32-BIT MICROPROCESSORS USER'S MANUAL
words of information are actually written to memory. The three
additional words are reserved for future use by Motorola.
.
15 14 13 12 11 10
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1000
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INSTRUCTION INPUT BUFFER
PROGRAM COUNTER (HIGH)
PROGRAM COUNTER (LOW)
SPECIAL STATUS WORD
FAULT ADDRESS (HIGH)
DATA OUTPUT BUFFER
FAULT ADDRESS (LOW)
UNUSED, RESERVED
UNUSED, RESERVED
UNUSED, RESERVED
DATA INPUT BUFFER
STATUS REGISTER
9
8
VECTOR OFFSET
7
6
5
4
3
2
1
0
MOTOROLA