MC68020RC20E Freescale Semiconductor, MC68020RC20E Datasheet - Page 68

• Manufacturer Part Number: MC68020RC20E
• Description: IC MICROPROCESSOR 32BIT 114-PGA
• Manufacturer: Freescale Semiconductor

Specifications of MC68020RC20E

• Processor Type: M680x0 32-Bit
• Speed: 20MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 114-PGA
• Family Name: M68000
• Device Core: ColdFire
• Device Core Size: 32b
• Frequency (max): 20MHz
• Instruction Set Architecture: RISC
• Supply Voltage 1 (typ): 5V
• Operating Supply Voltage (max): 5.25V
• Operating Supply Voltage (min): 4.75V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Through Hole
• Pin Count: 114
• Package Type: PGA
• Lead Free Status / RoHS Status: Contains lead / RoHS Compliant
• Features: -
• Lead Free Status / Rohs Status: Compliant

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Table 5-6 demonstrates that the processor always prefetches instructions by reading a
long word from a long-word address (A1, A0 = 00), regardless of port size or alignment.
When the required instruction begins at an odd-word boundary, the processor attempts to
fetch the entire 32 bits and loads both words into the instruction cache, if possible,
although the second one is the required word. Even if the instruction access is not cached,
the entire 32 bits are latched into an internal cache holding register from which the two
instructions words can subsequently be referenced. Refer to Section 8 Instruction
Execution Timing for a complete description of the cache holding register and pipeline
operation.
5.2.4 Address, Size, and Data Bus Relationships
The data transfer examples show how the MC68020/EC020 drives data onto or receives
data from the correct byte sections of the data bus. Table 5-7 shows the combinations of
the SIZ1, SIZ0, A1, and A0 signals that can be used to generate byte enable signals for
each of the four sections of the data bus for read and write cycles if the addressed device
requires them. The port size also affects the generation of these enable signals as shown
in the table. The four columns on the right correspond to the four byte enable signals.
Letters B, W, and L refer to port sizes: B for 8-bit ports, W for 16-bit ports, and L for 32-bit
ports. The letters B, W, and L imply that the byte enable signal should be true for that port
size. A dash (—) implies that the byte enable signal does not apply.
The MC68020/EC020 always drives all sections of the data bus because, at the beginning
of a write cycle, the bus controller does not know the port size.
Table 5-7 reveals that the MC68020/EC020 transfers the number of bytes specified by
SIZ1, SIZ0 to or from the specified address unless the operand is misaligned or unless the
number of bytes is greater than the port width. In these cases, the device transfers the
greatest number of bytes possible for the port. For example, if the size is four and A1, A0
= 01, a 32-bit slave can only receive three bytes in the current bus cycle. A 16- or 8-bit
slave can only receive one byte. The table defines the byte enables for all port sizes. Byte
data strobes can be obtained by combining the enable signals with the DS signal. Devices
residing on 8-bit ports can use the data strobe by itself since there is only one valid byte
for every transfer. These enable or strobe signals select only the bytes required for write
or read cycles. The other bytes are not selected, which prevents incorrect accesses in
sensitive areas such as I/O.
MOTOROLA
M68020 USER’S MANUAL
5- 21
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