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MC68341 USER’S MANUAL
MOTOROLA
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 block size. The block size is specified in the address mask register.
Both 8- and 16-Bit Ports Supported in M68300 Bus Cycle Mode
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 in M68300 bus mode. 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 (M68300 Bus Mode Only)
Programming the FTE, EDS, and DD bits 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 in M68300 mode.
Internal DSACK≈ Generation for External Accesses with Programmable Wait States
DSACK≈ can be generated internally with up to six wait states for a particular device
using the EDS and 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.
NOTE
If an access matches multiple chip selects, the lowest
numbered chip select will have priority. For example, if CS0
and CS2 "overlap" for a certain range, CS0 will assert when
accessing the "overlapped" address range, and CS2 will not.
Global chip select provides a 16-bit port with six wait states, which allows a boot ROM to
be located in any address space and still provide the stack pointer and program counter
values at $00000000 and $00000004, respectively. Global chip select does not provide
write protection and responds to all function codes. While CS0 is a global chip select, no
other chip select (CS7–CS1) can be used. CS0 operates in this manner until the V-bit is
set in the CS0 base address register, which will then allow the use of CS7–CS1. Provided
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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