MC68340 datasheet(52/441 Pages) FREESCALE

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MOTOROLA

MC68340 USER’S MANUAL

3- 3

Table 3-1. SIZx Signal Encoding

SIZ1

SIZ0

Transfer Size

Byte

Word

Three Bytes

Long Word

3.1.2 Function Code Signals

FC3–FC0 are outputs that indicate one of 16 address spaces to which the address

applies. Fifteen of these spaces are designated as either user or supervisor, program or

data, and normal or direct memory access (DMA) spaces. One other address space is

designated as CPU space to allow the CPU32 to acquire specific control information not

normally associated with read or write bus cycles. FC3–FC0 are valid while

AS is

asserted.

Function codes (see Table 3-2) can be considered as extensions of the 32-bit address

that can provide up to 16 different 4-Gbyte address spaces. Function codes are

automatically generated by the CPU32 to select address spaces for data and program at

both user and supervisor privilege levels, a CPU address space for processor functions,

and an alternate master address space. User programs access only their own program

and data areas to increase protection of system integrity and can be restricted from

accessing other information. The S-bit in the CPU32 status register is set for supervisor

accesses and cleared for user accesses to provide differentiation. Refer to 3.4 CPU

Space Cycles for more information.

Table 3-2. Address Space Encoding

Function Code Bits

3210

Address Spaces

0000

Reserved (Motorola)

0001

User Data Space

0010

User Program Space

0011

Reserved (User )

0100

Reserved (Motorola)

0101

Supervisor Data Space

0110

Supervisor Program Space

0111

CPU Space

DMA Space

Freescale Semiconductor, Inc.

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