MC68340 datasheet(111/441 Pages) FREESCALE

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MC68340 USER’S MANUAL

MOTOROLA

4.2.4.1 PROGRAMMABLE FEATURES. The chip select function supports the following

programmable features:

Four Programmable Chip Select Circuits

All four chip select circuits are independently programmable from the same list of

selectable features. Each chip select circuit has an individual base address register and

address mask register that contain the programmed characteristics of that chip select.

The base address register selects the starting address for the address block in 256-byte

increments. The address mask register specifies the size of the address block range.

The base address register V-bit indicates that the register information for that chip

select is valid. A global chip select (

CS0) allows address decode for a boot ROM before

system initialization occurs.

Variable Block Sizes

The block size, starting from the specified base address, can vary in size from 256

bytes up to 4 Gbytes in 2n increments. The specified base address must be on a

multiple of the the block size. The block size is specified in the address mask register.

Both 8- and 16-Bit Ports Supported

The 8-bit ports are accessible on both odd and even addresses when connected to data

bus bits 15–8; the 16-bit ports can be accessed as odd bytes, even bytes, or even

words. The port size is specified by the PS bits in the address mask register.

Write Protect Capability

The WP bit in each base address register can restrict write access to its range of

addresses.

Fast Termination Option

Programming the FTE bit in the base address register for the fast termination option

causes the chip select to terminate the cycle by asserting the internal

DSACK

≈ early,

providing a two-cycle external access.

Internal

DSACK

≈ Generation for External Accesses with Programmable Wait States

DSACK

≈ can be generated internally with up to three wait states for a particular device

using the DD bits in the address mask register.

Full 32-Bit Address Decode with Address Space Checking

The FC bits in the base address register and FCM bits in the address mask register are

used to select address spaces for which the chip selects will be asserted.

4.2.4.2 GLOBAL CHIP SELECT OPERATION. Global chip select operation allows

address decode for a boot ROM before system initialization occurs.

CS0 is the global chip

select output, and its operation differs from the other external chip select outputs following

reset. When the CPU32 begins fetching after reset,

CS0 is asserted for every address

until the V-bit is set in the

CS0 base address register.

Freescale Semiconductor, Inc.

For More Information On This Product,

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