mc68hc916y3 Freescale Semiconductor, Inc, mc68hc916y3 Datasheet - Page 173

• Manufacturer Part Number: mc68hc916y3
• Description: Mc68hc16y3 16 Bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

5.9.1.3 Chip-Select Option Registers
MC68HC16Y3/916Y3
USER’S MANUAL
The chip-select address compare logic uses only the most significant bits to match an
address within a block. The value of the base address must be an integer multiple of
the block size.
Because the logic state of ADDR[23:20] follows that of ADDR19 in the CPU16, maxi-
mum block size is 512 Kbytes. Because ADDR[23:20] follow the logic state of
ADDR19, addresses from $080000 to $F7FFFF are inaccessible.
After reset, the MCU fetches the initialization routine from the address contained in the
reset vector, located beginning at address $000000 of program space. To support
bootstrap operation from reset, the base address field in the boot chip-select base
address register (CSBARBT) has a reset value of $000, which corresponds to a base
address of $000000 and a block size of 512 Kbytes. A memory device containing the
reset vector and initialization routine can be automatically enabled by CSBOOT after
a reset. Refer to 5.9.4 Chip-Select Reset Operation for more information.
Option register fields determine timing of and conditions for assertion of chip-select
signals. To assert a chip-select signal, and to provide DSACK or autovector support,
other constraints set by fields in the option register and in the base address register
must also be satisfied. The following paragraphs summarize option register functions.
Refer to D.2.27 Chip-Select Option Registers for register and bit field information.
The MODE bit determines whether chip-select assertion simulates an asynchronous
bus cycle, or is synchronized to the M6800-type bus clock signal ECLK available on
ADDR23. Refer to 5.3 System Clock for more information on ECLK.
NOTES:
1. ADDR[23:20] are the same logic level as ADDR19 during normal
BLKSZ[2:0]
operation.
000
001
010
011
100
101
110
111
Freescale Semiconductor, Inc.
For More Information On This Product,
Table 5-24 Block Size Encoding
Go to: www.freescale.com
Block Size
128 Kbytes
256 Kbytes
512 Kbytes
512 Kbytes
16 Kbytes
64 Kbytes
2 Kbytes
8 Kbytes
Address Lines Compared
ADDR[23:11]
ADDR[23:13]
ADDR[23:14]
ADDR[23:16]
ADDR[23:17]
ADDR[23:18]
ADDR[23:19]
ADDR[23:20]
1
MOTOROLA
5-65